@article{xu_semenov_kim_2024, title={Voltage control of electromagnetic properties in antiferromagnetic materials}, volume={57}, ISSN={["1361-6463"]}, DOI={10.1088/1361-6463/ad3375}, abstractNote={Abstract}, number={24}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, author={Xu, Xinyi and Semenov, Yuriy G. and Kim, Ki Wook}, year={2024}, month={Jun} }
 @article{semenov_xu_boulton_kim_2023, title={Electrical control of Dzyaloshinskii-Moriya interactions in magnetic Weyl semimetals}, volume={108}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.108.134428}, abstractNote={The Dzyaloshinskii-Moriya interaction (DMI) is known to be responsible for multiple phenomena in magnetic materials. In the conventional description as a perturbation of the superexchange interaction by the spin-orbit coupling, the strength of the DMI is only weakly sensitive to the external fields, making its control difficult in spintronic applications. In this work, we show that an electrical modulation of the DMI may actually be possible in magnetic Weyl semimetals (WSMs). Specifically, it is theoretically illustrated that an antisymmetric indirect spin-spin interaction identified recently as an alternative mechanism for the DMI can result in the desired sensitivity to the external electric and magnetic fields via a redistribution of Weyl fermions among nodes of opposite chirality. This chiral anomaly enabled approach becomes particularly prominent in WSMs with inversion symmetry, in which the conventional DMI is not allowed. Numerical estimations suggest that moderate electric and magnetic fields of $\ensuremath{\sim}{10}^{3}--{10}^{4}\phantom{\rule{0.16em}{0ex}}\mathrm{V}/\mathrm{cm}$ and $\ensuremath{\sim}1$ T can induce a sufficiently strong change in the DMI. The impact of this externally modulated DMI on the manipulation of magnetic textures, including skyrmions in WSMs, is also discussed.}, number={13}, journal={PHYSICAL REVIEW B}, author={Semenov, Yuriy G. and Xu, Xinyi and Boulton, James A. and Kim, Ki Wook}, year={2023}, month={Oct} }
 @article{semenov_kim_2023, title={Electrical control of antiferromagnetic domain walls in Weyl semimetals}, volume={107}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.107.094434}, abstractNote={The electric-field-induced angular force on the N\'eel vector in antiferromagnetic (AFM) Weyl semimetals (WSMs) is theoretically investigated. Unlike in the ferromagnetic (FM) counterparts, the magnetic textures in the AFM WSMs, such as the domain walls (DWs) appear to lack the torsion in the magnetization and, thus, unable to benefit from this highly efficient mechanism that originates from the axial magnetic effect. Contrarily, our calculations illustrate that the addition of the Dzyaloshinskii-Morya interaction can introduce a twist in the magnetization around the DW location, giving rise to a nonzero axial magnetic field. This axial magnetic field, when combined with an external electric field, can lead to an imbalance in the fermion density of Weyl cones of opposite chirality and, thus, a spatially localized net electron spin polarization. The resulting effective exchange field can exert an angular force on the AFM textures for spatial movement, which can be significant in certain AFM WSMs even under a moderate external electric field. The dynamics of the DW motion under this emergent angular force is analyzed by considering the balance of energy absorption and dissipation. Our investigation reveals the need to account for the contribution of the exchange dissipation mechanism beyond the typical Gilbert-like (relativistic) term to compensate the unusual superlinear rate of energy absorption by the AFM textures. The obtained DW velocity vs electric-field characteristics show a significant speedup for the N\'eel DWs in the AFM WSMs over the counterparts in the FM WSMs as well as those in the nontopological magnets. The analysis also elucidates the dependence of the DW motion on the DW chirality in these materials. Our results clearly indicate the significance of the energy-efficient axial magnetic effect in the dynamics of spin textures in AFM WSMs with broken inversion symmetry.}, number={9}, journal={PHYSICAL REVIEW B}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2023}, month={Mar} }
 @article{stephanovich_kirichenko_engel_semenov_kim_2021, title={Carrier-induced ferromagnetism in two-dimensional magnetically doped semiconductor structures}, volume={104}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.104.094423}, abstractNote={We show theoretically that the magnetic ions, randomly distributed in a two-dimensional (2D) semiconductor system, can generate a ferromagnetic long-range order via the RKKY interaction. The main physical reason is the discrete (rather than continuous) symmetry of the 2D Ising model of the spin-spin interaction mediated by the spin-orbit coupling of 2D free carriers, which precludes the validity of the Mermin-Wagner theorem. Further, the analysis clearly illustrates the crucial role of the molecular field fluctuations as opposed to the mean field. The developed theoretical model describes the desired magnetization and phase-transition temperature $T_c$ in terms of a single parameter; namely, the chemical potential $\mu$. Our results highlight a path way to reach the highest possible $T_c$ in a given material as well as an opportunity to control the magnetic properties externally (e.g., via a gate bias). Numerical estimations show that magnetic impurities such as Mn$^{2+}$ with spins $S=5/2$ can realize ferromagnetism with $T_c$ close to room temperature.}, number={9}, journal={PHYSICAL REVIEW B}, author={Stephanovich, V. A. and Kirichenko, E. and Engel, G. and Semenov, Yu G. and Kim, K. W.}, year={2021}, month={Sep} }
 @article{kochelap_sokolov_kim_2021, title={Domains of electrically induced valley polarization in two-dimensional Dirac semiconductors}, volume={104}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.104.075403}, abstractNote={Electrically induced formation of valley-polarized free-carrier domains is theoretically investigated in two-dimensional (2D) honeycomb lattice systems exhibiting topological valley transport and the valley Hall effect. The results show that under a strong electric field $E$ applied along a nanostrip, the domains can be formed across the strip when this transverse dimension is comparable to the intervalley diffusion length ${L}_{iv}$. Further, these domains are found to be characterized by two distinct length scales dependent on $E$ and ${L}_{iv}$, i.e., the extended diffusion length ${L}_{\mathrm{ext}}$ ($\ensuremath{\propto}{L}_{iv}E$) and the compressed diffusion length ${L}_{\mathrm{com}}$ ($\ensuremath{\propto}{L}_{iv}/E$). The former determines the extension of the domain plateaus, whereas the latter specifies the width of the domain wall. Within each of the domains (excluding a narrow region of the domain wall; ${L}_{\mathrm{ext}}\ensuremath{\gg}{L}_{\mathrm{com}}$), the charge carriers are fully polarized belonging to only one of the valleys, providing a pure bulk valley current inside the considered domain region. The domain properties including the polarization amplitude and domain wall position are analyzed as a function of the applied electric field and intervalley scattering rates at the edges. The position of the domain wall, which determines the relative extension of the plateaus, can be controlled by a transverse current flowing between the Hall-type contacts. The current-voltage characteristic demonstrates a superlinear behavior in the range of electric fields corresponding to the valley-polarization domain formation. This feature is a distinctive signature of the anomalous transport arising from Bloch-band Berry curvature, which enhances the longitudinal conductance and diminishes the channel resistance. By reversing the applied electric field, the valley polarization and localization of the valley-polarized currents can be abruptly switchable. We suggest that the studied scheme of electrically induced domains of valley polarization in the 2D honeycomb lattice systems can be used in novel applications with all-electrical control and manipulation of the valley degree of freedom.}, number={7}, journal={PHYSICAL REVIEW B}, author={Kochelap, V. A. and Sokolov, V. N. and Kim, K. W.}, year={2021}, month={Aug} }
 @article{pan_mullen_kim_2021, title={First-principles analysis of magnetically doped transition-metal dichalcogenides}, volume={54}, ISSN={["1361-6463"]}, DOI={10.1088/1361-6463/abbb48}, abstractNote={Abstract}, number={2}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, author={Pan, Minghao and Mullen, Jeffrey T. and Kim, Ki Wook}, year={2021}, month={Jan} }
 @article{el-sherif_briggs_bersch_pan_hamidinejad_rajabpour_filleter_kim_robinson_bassim_2021, title={Scalable Characterization of 2D Gallium-Intercalated Epitaxial Graphene}, volume={13}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.1c14091}, abstractNote={Scalable synthesis of two-dimensional gallium (2D-Ga) covered by graphene layers was recently realized through confinement heteroepitaxy using silicon carbide substrates. However, the thickness, uniformity, and area coverage of the 2D-Ga heterostructures have not previously been studied with high-spatial resolution techniques. In this work, we resolve and measure the 2D-Ga heterostructure thicknesses using scanning electron microscopy (SEM). Utilizing multiple correlative methods, we find that SEM image contrast is directly related to the presence of uniform bilayer Ga at the interface and a variation of the number of graphene layers. We also investigate the origin of SEM contrast using both experimental measurements and theoretical calculations of the surface potentials. We find that a carbon buffer layer is detached due to the gallium intercalation, which increases the surface potential as an indication of the 2D-Ga presence. We then scale up the heterostructure characterization over a few-square millimeter area by segmenting SEM images, each acquired with nanometer-scale in-plane resolution. This work leverages the spectroscopic imaging capabilities of SEM that allows high-spatial resolution imaging for tracking intercalants, identifying relative surface potentials, determining the number of 2D layers, and further characterizing scalability and uniformity of low-dimensional materials.}, number={46}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={El-Sherif, Hesham and Briggs, Natalie and Bersch, Brian and Pan, Minghao and Hamidinejad, Mahdi and Rajabpour, Siavash and Filleter, Tobin and Kim, Ki Wook and Robinson, Joshua and Bassim, Nabil D.}, year={2021}, month={Nov}, pages={55428–55439} }
 @article{semenov_kim_2021, title={Spin-transfer and fieldlike torques in antiferromagnets}, volume={104}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.104.174402}, abstractNote={The phenomenon of spin-transfer torque (STT) in an antiferromagnet (AFM) is reexamined in terms of the incoming and outgoing spin currents. In contrast to the conventional approach, our model treats the STT as a result of the electron spin angular momentum transfer to the entire monodomain magnetic structure rather than to the individual sublattice magnetizations. This treatment enables the analysis to account for not only the destructive role of electron spin relaxation but also the potentially incomplete loss of electron spin phases that can either enhance the STT or suppress it depending on the structure parameters. Application of the developed model to the dynamical equation of the AFM order parameter illustrates the qualitative and quantitative differences with the conventional approach. Unlike the latter, our results predict a strong dependence of the STT on the orientation of the electron spin polarization relative to the magnetic anisotropy axes of the AFM. A similar characteristic also reveals a complex interplay in the N\'eel vector dynamics that can lead to a sublinear response of the oscillation frequency to the strength of the spin current. The impact of the fieldlike torque that can arise likewise from the spin injection is examined as well for a comprehensive account. The numerical calculations elucidate further the conditions that can elicit efficient manipulation of the magnetic states in an AFM under a spin-polarized current.}, number={17}, journal={PHYSICAL REVIEW B}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2021}, month={Nov} }
 @article{semenov_kim_2020, title={Efficient Control of Stochastic Switching via Spin Pumping in Antiferromagnetic Structures}, volume={13}, ISSN={["2331-7019"]}, DOI={10.1103/PhysRevApplied.13.064065}, abstractNote={Electrically controlled switching in an antiferromagnet (AFM), utilizing a currentless mechanism, is theoretically examined at finite temperatures. The structure consists of a metallic AFM with biaxial magnetic anisotropy sandwiched between a ferromagnetic spin filter and a semiconductor Schottky junction in a two-terminal pillar configuration. The calculations show that the torque necessary for the desired ${90}^{\ensuremath{\circ}}$ rotation of the N\'eel vector between two easy axes can be provided efficiently by pumping spin-polarized electrons into and out of the AFM through the metallic ferromagnetic layer. Consideration of thermal fluctuations illustrates the stochastic nature of the switching, whose probability distribution can be tailored by the electrical signal pulse as well as by the device dimensions. Detection of the N\'eel-vector state following this rotation may also be achieved straightforwardly via the large anisotropic magnetoresistance of the biaxial antiferromagnetic material. These properties, along with an ultrafast switching speed and a low energy requirement, are expected to be well suited for applications in nonvolatile memory and probabilistic computing.}, number={6}, journal={PHYSICAL REVIEW APPLIED}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2020}, month={Jun} }
 @misc{semenov_kim_2020, title={Modeling of Antiferromagnetic Dynamics: A Brief Review}, volume={14}, ISSN={["1942-7808"]}, DOI={10.1109/MNANO.2020.3024384}, abstractNote={This article briefly summarizes the basic principles of several theoretical models that are currently available for the description of antiferromagnetic dynamical response to external forces. The preference is given to simplified phenomenological treatments rather than the rigorous derivation of formalisms. In particular, the origin of ferromagnetic and antiferromagnetic correlations between localized spin moments is examined qualitatively for the simplest models as an introduction to the more sophisticated treatments. An emphasis is placed on elucidating the physical principles underlying the different mechanisms for electrical manipulation of the antiferromagnetic vector. More specifically, the current-induced torques via the spin transfer and the spinorbital interaction are described in a phenomenological manner. In addition, two prospective mechanisms for currentless generation of the desired spin torque are considered as promising alternatives. Following the overall focus, some of the intricate details are not addressed as they are outside the scope of this article.}, number={6}, journal={IEEE NANOTECHNOLOGY MAGAZINE}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2020}, month={Dec}, pages={32–41} }
 @article{regan_semenov_kim_2020, title={Optical bistability and self-opacity in magnetically doped monolayer transition metal dichalcogenides}, volume={102}, ISSN={["2469-9969"]}, DOI={10.1103/PhysRevB.102.214426}, abstractNote={Magneto-optical control of optical absorption spectra is theoretically investigated in two-dimensional (2D) dilute magnetic semiconductors such as monolayer transition metal dichalcogenides (TMDs) doped with magnetic ions. The underlying mechanism relies on efficient spin transfer between spin-polarized photoexcited carriers and localized magnetic ions via exchange scattering, and subsequent shifts in the electronic band structure induced by the resulting time-reversal symmetry breaking. A self-consistent model based on a rate equation is developed to analyze dynamical polarization of itinerant carrier spins and localized magnetic moments under circularly polarized optical excitation and the corresponding band modifications. The results illustrate that nonlinear effects such as optical bistability and self-opacity can indeed be achieved efficiently for a range of excitation power and frequency. In particular, the addition of magnetic dopants is shown to reduce the optical power required for the necessary band shifts by four orders of magnitude compared to that via the optical Stark effect in a nonmagnetic counterpart. Further investigation in a multidimensional parameter space elucidates the conditions for practical realization of the desired nonlinear effects in 2D TMD monolayers.}, number={21}, journal={PHYSICAL REVIEW B}, author={Regan, Malcolm J. and Semenov, Yuriy G. and Kim, Ki Wook}, year={2020}, month={Dec} }
 @article{xu_semenov_kim_2020, title={Spin wave generation via localized spin-orbit torque in an antiferromagnet-topological insulator heterostructure}, volume={128}, ISSN={["1089-7550"]}, DOI={10.1063/5.0010478}, abstractNote={The spin–orbit torque induced by a topological insulator (TI) is theoretically examined for spin wave generation in a neighboring antiferromagnetic thin film. The investigation is based on the micromagnetic simulation of Néel vector dynamics and the analysis of transport properties in the TI. The results clearly illustrate that propagating spin waves can be achieved in the antiferromagnetic thin-film strip through localized excitation, traveling over a long distance. The oscillation amplitude gradually decays due to the non-zero damping as the Néel vector precesses around the magnetic easy axis with a fixed frequency. The frequency is also found to be tunable via the strength of the driving electrical current density. While both the bulk and the surface states of the TI contribute to induce the effective torque, the calculation indicates that the surface current plays a dominant role over the bulk counterpart except in the heavily degenerate cases. Compared to the more commonly applied heavy metals, the use of a TI can substantially reduce the threshold current density to overcome the magnetic anisotropy, making it an efficient choice for spin wave generation. The Néel vector dynamics in the nano-oscillator geometry are examined as well.}, number={4}, journal={JOURNAL OF APPLIED PHYSICS}, author={Xu, Xinyi and Semenov, Yuriy G. and Kim, Ki Wook}, year={2020}, month={Jul} }
 @article{semenov_duan_li_kim_2019, title={Conductance nonreciprocity on the surface of a topological insulator with magnetic electrodes}, volume={128}, ISSN={["1879-2553"]}, DOI={10.1016/j.jpcs.2017.07.020}, abstractNote={Asymmetric electrical conductance is theoretically demonstrated on the surface of a topological insulator (TI) in the limit of infinitesimally small forward and reverse biases between two spin selective electrodes. The discontinuous behavior relies on the spin-momentum interlocked nature of TI surface electrons together with the resulting imbalance in the coupling coefficients between the electrodes and TI surface states. The analysis is based on a transmission matrix model that, in combination with a phenomenological treatment for the diffusive limit, accounts for both ballistic and scattered paths simultaneously. With the estimated conductance asymmetry over a factor of 10, implementations in the ratchet-like applications and low-voltage rectification circuits are potentially practicable.}, journal={JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS}, author={Semenov, Yuriy G. and Duan, Xiaopeng and Li, Xi-Lai and Kim, Ki Wook}, year={2019}, month={May}, pages={196–201} }
 @article{semenov_xu_kim_2019, title={Controllable Dispersion of Domain-Wall Movement in Antiferromagnetic Thin Films at Finite Temperatures}, volume={11}, ISSN={["2331-7019"]}, DOI={10.1103/PhysRevApplied.11.064051}, abstractNote={The dynamics of a 90$^{\circ }$ domain wall in an antiferromagnetic nanostrip driven by the current-induced spin-orbital torque are theoretically examined in the presence of random thermal fluctuations. A soliton-type equation of motion is developed on the basis of energy balance between the driving forces and dissipative processes in terms of the domain wall velocity. Comparison with micromagnetic simulations in the deterministic conditions shows good agreement in both the transient and steady-state transport. When the effects of random thermal fluctuations are included via a stochastic treatment, the results clearly indicate that the dispersion in the domain wall position can be controlled electrically by tailoring the strength and duration of the driving current mediating the spin orbital torque in the antiferromagnet. More specifically, the standard deviation of the probability distribution function for the domain wall movement can be tuned widely while maintaining the average position unaffected. Potential applications of this unusual functionality include the probabilistic computing such as Bayesian learning.}, number={6}, journal={PHYSICAL REVIEW APPLIED}, author={Semenov, Yuriy G. and Xu, Xinyi and Kim, Ki Wook}, year={2019}, month={Jun} }
 @article{xu_li_semenov_kim_2019, title={Creation and Destruction of Skyrmions via Electrical Modulation of Local Magnetic Anisotropy in Magnetic Thin Films}, volume={11}, ISSN={["2331-7019"]}, DOI={10.1103/PhysRevApplied.11.024051}, abstractNote={Magnetic skyrmions are topologically protected spin textures that are promising as carriers of information for computing and storage beyond CMOS-based systems. An electrostatic approach to creating a skyrmion can be more energy efficient than those based on a driving current. In this work, formation and dissolution of N\'eel skyrmions are examined theoretically via electrical modulation of magnetic anisotropy, in both ferromagnetic and antiferromagnetic structures. Simulations clearly illustrate the feasibility of the mechanism, enabling local control for versatility in applications. Also noteworthy is that the dynamical processes involved are much faster in antiferromagnetic materials.}, number={2}, journal={PHYSICAL REVIEW APPLIED}, author={Xu, Xinyi and Li, Xi-Lai and Semenov, Yuriy G. and Kim, Ki Wook}, year={2019}, month={Feb} }
 @article{xu_semenov_kim_2019, title={Electrical generation and propagation of spin waves in antiferromagnetic thin-film nanostrips}, volume={114}, ISSN={["1077-3118"]}, DOI={10.1063/1.5094767}, abstractNote={Electrical generation of terahertz spin waves is theoretically explored in an antiferromagnetic nanostrip via the current-induced spin–orbit torque. The analysis based on micromagnetic simulations clearly illustrates that the Néel-vector oscillations excited at one end of the magnetic strip can propagate in the form of a traveling wave when the nanostrip axis aligns with the magnetic easy-axis. A sizable threshold is observed in the driving current density or the torque to overcome the unfavorable anisotropy as expected. The generated spin waves are found to travel over a long distance, while the angle of rotation undergoes continuous decay in the presence of nonzero damping. The oscillation frequency is tunable via the strength of the spin–orbit torque, reaching the terahertz regime. Other key characteristics of spin waves such as the phase and the chirality can also be modulated actively. The simulation results further indicate the possibility of wavelike superposition between the excited spin oscillations, illustrating its application as an efficient source of spin-wave signals for information processing.}, number={23}, journal={APPLIED PHYSICS LETTERS}, author={Xu, Xinyi and Semenov, Yuriy G. and Kim, Ki Wook}, year={2019}, month={Jun} }
 @article{kochelap_korotyeyev_lyashchuk_kim_2019, title={Nanoscale ballistic diodes made of polar materials for amplification and generation of radiation in the 10 THz-range}, volume={126}, ISSN={["1089-7550"]}, DOI={10.1063/1.5117220}, abstractNote={We investigate ultrahigh frequency electrical properties of nanoscale n+−i−n+ diodes made of polar semiconductors. The calculations show that the coupling between optical vibrations of the lattice and the ballistic electrons strongly modifies and enhances the time-of-flight effects giving rise to narrow resonances of the diode impedance in the reststrahlen frequency range. Particularly, negative dynamic resistance is induced in close proximity to the optical phonon frequency. The resonant effects in the dynamic resistance of nanoscale GaAs and InP diodes are studied in detail. The obtained magnitudes of the negative dynamic resistance effect indicate that the nanoscale diodes are capable of generating electromagnetic radiation in the far-infrared spectral range under electric pumping.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Kochelap, V. A. and Korotyeyev, V. V. and Lyashchuk, Yu. M. and Kim, K. W.}, year={2019}, month={Aug} }
 @article{semenov_xu_kim_2019, title={Thermal fluctuations in antiferromagnetic nanostructures}, volume={489}, ISSN={["1873-4766"]}, DOI={10.1016/j.jmmm.2019.165457}, abstractNote={A theoretical model is developed that can accurately analyze the effects of thermal fluctuations in antiferromagnetic (AFM) nano-particles. The approach is based on Fourier series representation of the random effective field with cut-off frequencies of physical origin at low and high limits while satisfying the fluctuation-dissipation theorem at the same time. When coupled with the formalism of a Langevin dynamical equation, it can describe the stochastic Néel vector dynamics with the AFM parameters, circumventing the arbitrariness of the commonly used treatments in the micro-magnetic simulations. Subsequent application of the model to spontaneous Néel vector switching provides a thermal stability analysis of the AFM states. The numerical simulation shows that the AFM states are much less prone to the thermally induced accidental flips than the ferromagnetic counterparts, suggesting a longer retention time for the former.}, journal={JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS}, author={Semenov, Yuriy G. and Xu, Xiniy and Kim, Ki Wook}, year={2019}, month={Nov} }
 @article{barra_domann_kim_carman_2018, title={Voltage Control of Antiferromagnetic Phases at Near-Terahertz Frequencies}, volume={9}, ISSN={2331-7019}, url={http://dx.doi.org/10.1103/PhysRevApplied.9.034017}, DOI={10.1103/PhysRevApplied.9.034017}, abstractNote={The recent push toward THz sensing, transduction, and memory has created a significant need for materials that operate above ferromagnetic resonance frequencies, which are typically in the low GHz range. Antiferromagnetic materials with THz resonances seem promising, but their lack of a net magnetic moment makes manipulating them difficult. Here a fully coupled magnetomechanical model is developed, showing that antiferromagnetic single domains are controllable via strain coupling. The results indicate that near-THz device response is possible with ultralow power consumption.}, number={3}, journal={Physical Review Applied}, publisher={American Physical Society (APS)}, author={Barra, Anthony and Domann, John and Kim, Ki Wook and Carman, Greg}, year={2018}, month={Mar} }
 @article{semenov_li_kim_2017, title={Currentless reversal of Néel vector in antiferromagnets}, volume={95}, ISSN={2469-9950 2469-9969}, url={http://dx.doi.org/10.1103/PhysRevB.95.014434}, DOI={10.1103/physrevb.95.014434}, abstractNote={The bias driven perpendicular magnetic anisotropy is a magneto-electric effect that can realize 90$^\circ$ magnetization rotation and even 180$% ^\circ $ flip along the easy axis in the ferromagnets with a minimal energy consumption. This study theoretically demonstrates a similar phenomenon of the Neel vector reversal via a short electrical pulse that can mediate perpendicular magnetic anisotropy in the antiferromagnets. The analysis based on the dynamical equations as well as the micro-magnetic simulations reveals the important role of the inertial behavior in the antiferromagnets that facilitates the Neel vector to overcome the barrier between two free-energy minima of the bistable states along the easy axis. In contrast to the ferromagnets, this Neel vector reversal does not accompany angular moment transfer to the environment, leading to acceleration in the dynamical response by a few orders of magnitude. Further, a small switching energy requirement of a few attojoules illustrates an added advantage of the phenomenon in low-power spintronic applications.}, number={1}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Li, Xi-Lai and Kim, Ki Wook}, year={2017}, month={Jan} }
 @article{narendra_norouzzadeh_vashaee_kim_2017, title={Doping induced enhanced density of states in bismuth telluride}, volume={111}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4989602}, DOI={10.1063/1.4989602}, abstractNote={Power factor enhancement through resonant doping is explored in Bi2Te3 based on a detailed first-principles study. Of the dopant atoms investigated, it is found that the formation of resonant states may be achieved with In, Po, and Na, leading potentially to a significant increase in the thermoelectric efficiency at room temperature. While doping with Po forms twin resonant state peaks in the valence and conduction bands, the incorporation of Na or In results in the resonant states close to the valence band edge. Further analysis reveals the origin of these resonant states. Transport calculations are also carried out to estimate the anticipated level of enhancement.}, number={23}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Narendra, Namita and Norouzzadeh, Payam and Vashaee, Daryoosh and Kim, Ki Wook}, year={2017}, month={Dec}, pages={232101} }
 @article{li_duan_semenov_kim_2017, title={Electrical switching of antiferromagnets via strongly spin-orbit coupled materials}, volume={121}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4974027}, DOI={10.1063/1.4974027}, abstractNote={Electrically controlled ultra-fast switching of an antiferromagnet (AFM) is shown to be realizable by interfacing it with a material of strong spin-orbit coupling. The proximity interaction between the sublattice magnetic moments of a layered AFM and the spin-polarized free electrons at the interface offers an efficient way to manipulate antiferromagnetic states. A quantitative analysis, using the combination with a topological insulator as an example, demonstrates highly reliable 90° and 180° rotations of AFM magnetic states under two different mechanisms of effective torque generation at the interface. The estimated switching speed and energy requirement are in the ps and aJ ranges, respectively, which are about two-three orders of magnitude better than the ferromagnetic counterparts. The observed differences in the magnetization dynamics may explain the disparate characteristic responses. Unlike the usual precessional/chiral motions in the ferromagnets, those of the AFMs can essentially be described as a damped oscillator with a more direct path. The impact of random thermal fluctuations is also examined.}, number={2}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Li, Xi-Lai and Duan, Xiaopeng and Semenov, Yuriy G. and Kim, Ki Wook}, year={2017}, month={Jan}, pages={023907} }
 @article{semenov_li_xu_kim_2017, title={Helical waves in easy-plane antiferromagnets}, volume={96}, ISSN={2469-9950 2469-9969}, url={http://dx.doi.org/10.1103/PhysRevB.96.224432}, DOI={10.1103/PhysRevB.96.224432}, abstractNote={Effective spin torques can generate the N\'eel vector oscillations in antiferromagnets (AFMs). Here, it is theoretically shown that these torques applied at one end of a normal AFM strip can excite a helical type of spin wave in the strip whose properties are drastically different from characteristic spin waves. An analysis based on both a N\'eel vector dynamical equation and the micromagnetic simulation identifies the direction of magnetic anisotropy and the damping factor as the two key parameters determining the dynamics. Helical wave propagation requires the hard axis of the easy-plane AFM to be aligned with the traveling direction, while the damping limits its spatial extent. If the damping is neglected, the calculation leads to a uniform periodic domain wall structure. On the other hand, finite damping decelerates the helical wave rotation around the hard axis, ultimately causing stoppage of its propagation along the strip. With the group velocity staying close to spin-wave velocity at the wave front, the wavelength becomes correspondingly longer away from the excitation point. In a sufficiently short strip, a steady-state oscillation can be established whose frequency is controlled by the waveguide length as well as the excitation energy or torque.}, number={22}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Li, Xi-Lai and Xu, Xinyi and Kim, Ki Wook}, year={2017}, month={Dec} }
 @article{semenov_kim_2017, title={Spin pumping torque in antiferromagnets}, volume={110}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4983196}, DOI={10.1063/1.4983196}, abstractNote={A currentless, magnetic-field free mechanism for the Néel vector rotation in an antiferromagnet is proposed. An efficient torque is induced by spin pumping through charging/discharging of spin filtered electrons via a ferromagnetic layer in a spin capacitor structure consisting of the two heterogenous magnetic materials. The relatively long electron spin relaxation time in the antiferromagnet enables the electron spin polarizations to retain the exchange effective field sufficiently long to modulate the local magnetic moments and subsequently the magnetic state of the material. Precession of the sublattice magnetization is modeled based on the Néel vector formulation, theoretically demonstrating the feasibility of the physical mechanism (such as the reversal) with sub-aJ energy consumption. Its potential application to spintronic devices is also discussed.}, number={19}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2017}, month={May}, pages={192405} }
 @article{narendra_kim_2017, title={Toward enhanced thermoelectric effects in Bi2Te3/Sb2Te3heterostructures}, volume={32}, ISSN={0268-1242 1361-6641}, url={http://dx.doi.org/10.1088/1361-6641/aa539d}, DOI={10.1088/1361-6641/aa539d}, abstractNote={The possibility of enhanced thermoelectric properties through nanostructuring is investigated theoretically in a p-type Bi2Te3/Sb2Te3 heterostructure. A multi-scale modeling approach is adopted to account for the atomistic characteristics of the interface as well as the carrier/phonon transport properties in the larger scales. The calculations clearly illustrate the desired impact of carrier energy filtering at the potential barrier by locally boosting the power factor over a sizable distance in the well region. Further, the phonon transport analysis illustrates a considerable reduction in the thermal conductivity at the heterointerface. Both effects are expected to provide an effective means to engineer higher zT in this material system.}, number={3}, journal={Semiconductor Science and Technology}, publisher={IOP Publishing}, author={Narendra, Namita and Kim, Ki Wook}, year={2017}, month={Jan}, pages={035005} }
 @article{mao_chen_kim_2016, title={Atomistic modeling of phonon transport in turbostratic graphitic structures}, volume={119}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4952703}, DOI={10.1063/1.4952703}, abstractNote={Thermal transport in turbostratic graphitic systems is investigated by using an atomistic analytical model based on the 4th-nearest-neighbor force constant approximation and a registry-dependent interlayer potential. The developed model is shown to produce an excellent agreement with the experimental data and ab initio results in the calculation of bulk properties. Subsequent analysis of phonon transport in combination with the Green's function method illustrates the significant dependence of key characteristics on the misorientation angle, clearly indicating the importance of this degree of freedom in multi-stacked structures. Selecting three angles with the smallest commensurate unit cells, the thermal resistance is evaluated at the twisted interface between two AB stacked graphite. The resulting values in the range of 35 × 10−10 K m2/W to 116 × 10−10 K m2/W are as large as those between two dissimilar material systems such as a metal and graphene. The strong rotational effect on the cross-plane thermal transport may offer an effective means of phonon engineering for applications such as thermoelectric materials.}, number={20}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Mao, Rui and Chen, Yifeng and Kim, Ki Wook}, year={2016}, month={May}, pages={204305} }
 @article{semenov_kim_2016, title={Bias-driven spontaneous spin-valley polarization in monolayer transition-metal dichalcogenides}, volume={93}, ISSN={2469-9950 2469-9969}, url={http://dx.doi.org/10.1103/PhysRevB.93.041414}, DOI={10.1103/physrevb.93.041414}, abstractNote={A physical mechanism that may enable electrical control of carrier spin-valley polarization is theoretically examined in a monolayer transition-metal dichalcogenide (TMD) structure. The idea is based on the interplay between the strongly spin-orbit coupled nature of the TMD band structure and the exchange interaction with a proximate magnet that can spontaneously lift the valley degeneracy when the carrier density exceeds a certain threshold. The analysis based on the free energy of the system clearly illustrates the desired spin-valley polarization in the TMD layer as well as the accompanying rotational phase transition in the magnetization. Numerical estimates utilizing the ${\mathrm{WS}}_{2}$ parameters as an example indicate a sharp transition in the spin-valley polarization over tens of percent at room temperature with only a modest change in the electrochemical potential of a few meV via electrostatic bias. Detection of the predicted phenomenon is expected to be straightforward through the corresponding modification in the TMD channel conductance.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Kim, Ki Wook}, year={2016}, month={Jan} }
 @inproceedings{li_duan_semenov_kim_2016, title={Electrically controlled switching of antiferromagnets via proximity interaction induced by topological insulator}, ISBN={9781509028283}, url={http://dx.doi.org/10.1109/drc.2016.7548494}, DOI={10.1109/drc.2016.7548494}, abstractNote={Here, we propose an electrical control of antiferromagnet (AFM) by utilizing the proximity interaction between a topological insulator (TI) and an AFM. Following the Bennett clocking scheme, this mechanism shows much faster switching speed and higher logic reliabilities compared to its ferromagnetic counterpart according to micro-magnetic simulations. Consequently, both switching period and power consumption are reduced by 2-3 orders of magnitude making the TI-AFM system a better candidate for spintronic applications.}, booktitle={2016 74th Annual Device Research Conference (DRC)}, publisher={IEEE}, author={Li, Xi-Lai and Duan, Xiaopeng and Semenov, Yuriy G. and Kim, Ki Wook}, year={2016}, month={Jun} }
 @article{jin_mullen_kim_2016, title={Highly anisotropic electronic transport properties of monolayer and bilayer phosphorene from first principles}, volume={109}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4960526}, DOI={10.1063/1.4960526}, abstractNote={The intrinsic carrier transport dynamics in phosphorene is theoretically examined. Utilizing a density functional theory treatment, the low-field mobility and the saturation velocity are characterized for both electrons and holes in the monolayer and bilayer structures. The analysis clearly elucidates the crystal orientation dependence manifested through the anisotropic band structure and the carrier-phonon scattering rates. In the monolayer, the hole mobility in the armchair direction is estimated to be approximately five times larger than in the zigzag direction at room temperature (460 cm2/V s vs. 90 cm2/V s). The bilayer transport, on the other hand, exhibits a more modest anisotropy with substantially higher mobilities (1610 cm2/V s and 760 cm2/V s, respectively). The calculations on the conduction-band electrons indicate a comparable dependence while the characteristic values are generally smaller by about a factor of two. The variation in the saturation velocity is found to be less pronounced. With the anticipated superior performance and the diminished anisotropy, few-layer phosphorene offers a promising opportunity particularly in p-type applications.}, number={5}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Jin, Zhenghe and Mullen, Jeffrey T. and Kim, Ki Wook}, year={2016}, month={Aug}, pages={053108} }
 @article{kukhtaruk_kochelap_sokolov_kim_2016, title={Spatially dispersive dynamical response of hot carriers in doped graphene}, volume={79}, ISSN={["1873-1759"]}, DOI={10.1016/j.physe.2015.12.008}, abstractNote={We study theoretically wave-vector and frequency dispersion of the complex dynamic conductivity tensor (DCT), σlm(k,ω), of doped monolayer graphene under a strong dc electric field. For a general analysis, we consider the weak ac field of arbitrary configuration given by two independent vectors, the ac field polarization and the wave vector k. The high-field transport and linear response to the ac field are described on the base of the Boltzmann kinetic equation. We show that the real part of DCT, calculated in the collisionless regime, is not zero due to dissipation of the ac wave, whose energy is absorbed by the resonant Dirac quasiparticles effectively interacting with the wave. The role of the kinematic resonance at ω=vF|k| (vF is the Fermi velocity) is studied in detail taking into account deviation from the linear energy spectrum and screening by the charge carriers. The isopower-density curves and distributions of angle between the ac current density and field vectors are presented as a map which provides clear graphic representation of the DCT anisotropy. Also, the map shows certain ac field configurations corresponding to a negative power density, thereby it indicates regions of terahertz frequency for possible electrical (drift) instability in the graphene system.}, journal={PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES}, author={Kukhtaruk, S. M. and Kochelap, V. A. and Sokolov, V. N. and Kim, K. W.}, year={2016}, month={May}, pages={26–37} }
 @article{duan_li_li_semenov_kim_2015, title={Highly efficient conductance control in a topological insulator based magnetoelectric transistor}, volume={118}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4937407}, DOI={10.1063/1.4937407}, abstractNote={The spin-momentum interlocked properties of the topological insulator (TI) surface states are exploited in a transistor-like structure for efficient conductance control in the TI-magnet system. Combined with the electrically induced magnetization rotation as part of the gate function, the proposed structure takes advantage of the magnetically modulated TI electronic band dispersion in addition to the conventional electrostatic barrier. The transport analysis coupled with the magnetic simulation predicts super-steep current-voltage characteristics near the threshold along with the GHz operating frequencies. Potential implementation to a complementary logic is also examined. The predicted characteristics are most suitable for applications requiring low power or those with small signals.}, number={22}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Duan, Xiaopeng and Li, Xi-Lai and Li, Xiaodong and Semenov, Yuriy G. and Kim, Ki Wook}, year={2015}, month={Dec}, pages={224502} }
 @article{duan_li_semenov_kim_2015, title={Nonlinear magnetic dynamics in a nanomagnet–topological insulator heterostructure}, volume={92}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.92.115429}, DOI={10.1103/physrevb.92.115429}, abstractNote={Magnetization dynamics of a nanomagnet, when strongly coupled with a topological insulator (TI) via the proximity interaction, is examined theoretically in the presence of electrical current on the TI surface under realistic transport conditions. Due to the spin-momentum interlock, the magnetic state and TI electron transport depend significantly on each other. Such an interdependence leads to a variety of nonlinear dynamical responses in all transport regimes including the scattering dominant diffusive cases. Generation of the anomalous Hall current, in particular, is found to be a key to the unique features that have not been observed previously. For instance, the anomalous Hall current can result in antiparallel alignment of the final magnetization state in reference to the effective driving magnetic field by inducing an extra term that counters the damping effect. Similarly the calculation also reveals steady oscillation of the magnetization under a broad range of conditions, offering a robust mechanism for highly efficient magnetization reversal and/or spin wave excitation under a dc bias.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Duan, Xiaopeng and Li, Xi-Lai and Semenov, Yuriy G. and Kim, Ki Wook}, year={2015}, month={Sep} }
 @article{jin_nori_lee_kumar_wu_prater_kim_narayan_2015, title={Strain induced room temperature ferromagnetism in epitaxial magnesium oxide thin films}, volume={118}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4934498}, DOI={10.1063/1.4934498}, abstractNote={We report on the epitaxial growth and room-temperature ferromagnetic properties of MgO thin films deposited on hexagonal c-sapphire substrates by pulsed laser deposition. The epitaxial nature of the films has been confirmed by both θ-2θ and φ-scans of X-ray diffraction pattern. Even though bulk MgO is a nonmagnetic insulator, we have found that the MgO films exhibit ferromagnetism and hysteresis loops yielding a maximum saturation magnetization up to 17 emu/cc and large coercivity, Hc = 1200 Oe. We have also found that the saturation magnetization gets enhanced and that the crystallization degraded with decreased growth temperature, suggesting that the origin of our magnetic coupling could be point defects manifested by the strain in the films. X-ray (θ-2θ) diffraction peak shift and strain analysis clearly support the presence of strain in films resulting from the presence of point defects. Based on careful investigations using secondary ion mass spectrometer and X-ray photoelectron spectroscopy studies, we have ruled out the possibility of the presence of any external magnetic impurities. We discuss the critical role of microstructural characteristics and associated strain on the physical properties of the MgO films and establish a correlation between defects and magnetic properties.}, number={16}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Jin, Zhenghe and Nori, Sudhakar and Lee, Yi-Fang and Kumar, D. and Wu, Fan and Prater, J. T. and Kim, Ki Wook and Narayan, Jagdish}, year={2015}, month={Oct}, pages={165309} }
 @article{li_duan_kim_2014, title={Controlling electron propagation on a topological insulator surface via proximity interactions}, volume={89}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.89.045425}, DOI={10.1103/physrevb.89.045425}, abstractNote={The possibility of electron beam guiding is theoretically explored on the surface of a topological insulator through the proximity interaction with a magnetic material. The electronic band modification induced by the exchange coupling at the interface defines the path of electron propagation in analogy to the optical fiber for photons. Numerical simulations indicate the guiding efficiency is much higher than that in the ``waveguide'' formed by an electrostatic potential barrier such as $p$-$n$ junctions. Furthermore, the results illustrate effective flux control and beam steering that can be realized by altering the magnetization/spin texture of the adjacent magnetic materials. Specifically, the feasibility to switch on and off and make a large-angle turn is demonstrated under realistic conditions. Potential implementation to logic and interconnect applications is also examined in connection with electrically controlled magnetization switching.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Li, Xiaodong and Duan, Xiaopeng and Kim, Ki Wook}, year={2014}, month={Jan} }
 @article{yu_hu_su_huang_liu_jin_purezky_geohegan_kim_zhang_et al._2014, title={Equally Efficient Interlayer Exciton Relaxation and Improved Absorption in Epitaxial and Nonepitaxial MoS2/WS2 Heterostructures}, volume={15}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl5038177}, DOI={10.1021/nl5038177}, abstractNote={Semiconductor heterostructures provide a powerful platform to engineer the dynamics of excitons for fundamental and applied interests. However, the functionality of conventional semiconductor heterostructures is often limited by inefficient charge transfer across interfaces due to the interfacial imperfection caused by lattice mismatch. Here we demonstrate that MoS(2)/WS(2) heterostructures consisting of monolayer MoS(2) and WS(2) stacked in the vertical direction can enable equally efficient interlayer exciton relaxation regardless the epitaxy and orientation of the stacking. This is manifested by a similar 2 orders of magnitude decrease of photoluminescence intensity in both epitaxial and nonepitaxial MoS(2)/WS(2) heterostructures. Both heterostructures also show similarly improved absorption beyond the simple superimposition of the absorptions of monolayer MoS(2) and WS(2). Our result indicates that 2D heterostructures bear significant implications for the development of photonic devices, in particular those requesting efficient exciton separation and strong light absorption, such as solar cells, photodetectors, modulators, and photocatalysts. It also suggests that the simple stacking of dissimilar 2D materials with random orientations is a viable strategy to fabricate complex functional 2D heterostructures, which would show similar optical functionality as the counterpart with perfect epitaxy.}, number={1}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Yu, Yifei and Hu, Shi and Su, Liqin and Huang, Lujun and Liu, Yi and Jin, Zhenghe and Purezky, Alexander A. and Geohegan, David B. and Kim, Ki Wook and Zhang, Yong and et al.}, year={2014}, month={Dec}, pages={486–491} }
 @article{mai_semenov_barrette_yu_jin_cao_kim_gundogdu_2014, title={Exciton valley relaxation in a single layer ofWS2measured by ultrafast spectroscopy}, volume={90}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.90.041414}, DOI={10.1103/physrevb.90.041414}, abstractNote={We measured the lifetime of optically created valley polarization in single layer WS2 using transient absorption spectroscopy. The electron valley relaxation is very short (< 1ps). However the hole valley lifetime is at least two orders of magnitude longer and exhibits a temperature dependence that cannot be explained by single carrier spin/valley relaxation mechanisms. Our theoretical analysis suggests that a collective contribution of two potential processes may explain the valley relaxation in single layer WS2. One process involves direct scattering of excitons from K to K' valleys with a spin flip-flop interaction. The other mechanism involves scattering through spin degenerate Gamma valley. This second process is thermally activated with an Arrhenius behavior due to the energy barrier between Gamma and K valleys.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Mai, Cong and Semenov, Yuriy G. and Barrette, Andrew and Yu, Yifei and Jin, Zhenghe and Cao, Linyou and Kim, Ki Wook and Gundogdu, Kenan}, year={2014}, month={Jul} }
 @article{kong_jin_kim_2014, title={Hot-Electron Transistors for Terahertz Operation Based on Two-Dimensional Crystal Heterostructures}, volume={2}, ISSN={2331-7019}, url={http://dx.doi.org/10.1103/PhysRevApplied.2.054006}, DOI={10.1103/physrevapplied.2.054006}, abstractNote={The authors explore the feasibility of ultrahigh-frequency devices by utilizing the unique features of two-dimensional (2D) crystals. These materials range from gapless semimetals to wide-band-gap insulators, and a number of them ($e.g.$ hexagonal boron nitride and transition metal dichalcogenides) can be integrated seamlessly with graphene, without causing defects, interfacial scattering centers, or degradation of properties. A detailed theoretical analysis indicates the potential for 2D crystal heterostructures that could process information at rates well over a terahertz--several times the current technological limit.}, number={5}, journal={Physical Review Applied}, publisher={American Physical Society (APS)}, author={Kong, Byoung Don and Jin, Zhenghe and Kim, Ki Wook}, year={2014}, month={Nov} }
 @article{jin_li_mullen_kim_2014, title={Intrinsic transport properties of electrons and holes in monolayer transition-metal dichalcogenides}, volume={90}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.90.045422}, DOI={10.1103/physrevb.90.045422}, abstractNote={Intrinsic electron- and hole-phonon interactions are investigated in monolayer transition-metal dichalcogenides $M{X}_{2}$ (M=Mo, W; X=S, Se) based on a density functional theory formalism. Due to their structural similarities, all four materials exhibit qualitatively comparable scattering characteristics with the acoustic phonons playing a dominant role near the conduction and valence band extrema at the K point. However, substantial differences are observed quantitatively leading to disparate results in the transport properties. Of those considered, ${\mathrm{WS}}_{2}$ provides the best performance for both electrons and holes with high mobilities and saturation velocities in the full-band Monte Carlo analysis of the Boltzmann transport equation. It is also found that monolayer $M{X}_{2}$ crystals with an exception of ${\mathrm{MoSe}}_{2}$ generally show hole mobilities comparable to or even larger than the value for bulk silicon at room temperature, suggesting a potential opportunity in p-type devices. The analysis is extended to estimate the effective deformation potential constants for a simplified treatment as well.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Jin, Zhenghe and Li, Xiaodong and Mullen, Jeffrey T. and Kim, Ki Wook}, year={2014}, month={Jul} }
 @inproceedings{duan_li_semenov_kim_2014, title={Proposal of a topological insulator based magnetoelectric transistor}, DOI={10.1109/drc.2014.6872341}, abstractNote={A new type of transistor is proposed based on wave-guiding phenomena of topological insulator (TI) surface electrons for applications in CMOS-like circuits and switchable interactions in spin logic circuits. The carrier channel is patterned by the magnetic strip and the ON/OFF switch is achieved by the electrically controlled magnetic valve (Fig. 1A). We characterized the current-gate voltage (Id-Vg) relation and the time resolved performance. Very low subthreshold swing (below 10 mV/dec) and operating frequency above 1 GHz are expected.}, booktitle={2014 72nd annual device research conference (drc)}, author={Duan, X. P. and Li, X. D. and Semenov, Y. G. and Kim, K. W.}, year={2014}, pages={149–150} }
 @article{duan_li_semenov_kim_2014, title={Quasi-optical electron transport across a magnetically induced junction on a topological insulator surface}, volume={116}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4903798}, DOI={10.1063/1.4903798}, abstractNote={Quasi-optical Dirac electron transport is theoretically analyzed at the magnetic boundaries on a topological insulator (TI) surface. The electronic band mismatch induced by the spatially varying magnetization profile can form an effective junction akin to the electrostatic potential step. The transmission/reflection characteristics show a direct dependence on electron energy and incident angle with highly asymmetric patterns. The investigation also illustrates a nontrivial anomalous Hall current along the boundary which is further shown by a numerical simulation based on the finite-difference time-domain method. The results provide key design guidelines for prospective quasi-optical devices based on the TI-magnet heterostructures.}, number={22}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Duan, Xiaopeng and Li, Xiaodong and Semenov, Yuriy G. and Kim, Ki Wook}, year={2014}, month={Dec}, pages={224301} }
 @article{duan_semenov_kim_2014, title={Spin Logic via Controlled Correlation in Nanomagnet–Dirac-Fermion Heterostructures}, volume={2}, ISSN={2331-7019}, url={http://dx.doi.org/10.1103/PhysRevApplied.2.044003}, DOI={10.1103/physrevapplied.2.044003}, abstractNote={A hybrid structure combining the advantages of topological insulator (TI), dielectric ferromagnet (FM), and graphene is investigated to realize the electrically controlled correlation between electronic and magnetic subsystems for low-power, high-functional applications. Two-dimensional Dirac fermion states provide an ideal environment to facilitate strong coupling through the surface interactions with proximate materials. The unique properties of FM-TI and FM-graphene interfaces make it possible for active "manipulation" and "propagation", respectively, of the information state variable based solely on the spin logic platform through electrical gate biases. Our theoretical analysis verifies the feasibility of the concept for logic application with both current-driven and current-less interconnect approaches. The device/circuit characteristics are also examined in realistic conditions, suggesting the desired low-power performance with the estimated energy consumption for COPY/NOT as low as the \textit{attojoule} level.}, number={4}, journal={Physical Review Applied}, publisher={American Physical Society (APS)}, author={Duan, Xiaopeng and Semenov, Yuriy G. and Kim, Ki Wook}, year={2014}, month={Oct} }
 @article{mao_kong_kim_2014, title={Thermal transport properties of metal/MoS2 interfaces from first principles}, volume={116}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4890347}, DOI={10.1063/1.4890347}, abstractNote={Thermal transport properties at the metal/MoS2 interfaces are analyzed by using an atomistic phonon transport model based on the Landauer formalism and first-principles calculations. The considered structures include chemisorbed Sc(0001)/MoS2 and Ru(0001)/MoS2, physisorbed Au(111)/MoS2, as well as Pd(111)/MoS2 with intermediate characteristics. Calculated results illustrate a distinctive dependence of thermal transfer on the details of interfacial microstructures. More specifically, the chemisorbed case with a stronger bonding exhibits a generally smaller interfacial thermal resistance than the physisorbed. Comparison between metal/MoS2 and metal/graphene systems suggests that metal/MoS2 is significantly more resistive. Further examination of lattice dynamics identifies the presence of multiple distinct atomic planes and bonding patterns at the interface as the key origins of the observed large thermal resistance.}, number={3}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Mao, Rui and Kong, Byoung Don and Kim, Ki Wook}, year={2014}, month={Jul}, pages={034302} }
 @article{li_semenov_kim_2014, title={Thin-film topological insulator-ferromagnet heterostructures for terahertz detection}, volume={104}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4865423}, DOI={10.1063/1.4865423}, abstractNote={An atomically thin topological insulator is investigated theoretically for long-wavelength photodetection when it interacts with a magnetic material. Through the coupling between top and bottom surfaces as well as the exchange interaction with the proximate ferromagnet, the distribution of optically excited carriers exhibits unique patterns that depend sensitively on the frequency of the incoming light. This effect results in the generation of strong nonzero photocurrent, leading potentially to room-temperature detection of far-infrared/THz radiation with the advantage of low noise and fast response. The ease of frequency tuning by an external electrical bias offers an added versatility in the realistic implementation.}, number={6}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Li, Xiaodong and Semenov, Yuriy G. and Kim, Ki Wook}, year={2014}, month={Feb}, pages={061116} }
 @inproceedings{barrette_mai_yu_semenov_jin_kim_cao_gundogdu_2014, title={Ultrafast valley relaxation dynamics in single layer semiconductors}, url={http://dx.doi.org/10.1117/12.2062401}, DOI={10.1117/12.2062401}, abstractNote={Single layer transition metal dichalcogenides are 2D semiconducting systems with unique electronic band structure. Two-valley energy bands along with strong spin-orbital coupling lead to valley-dependent carrier spin polarization, which is the basis for recently proposed valleytronic applications. These systems also exhibit unusually strong many body effects, such as strong exciton and trion binding, due to reduced dielectric screening of Coulomb interactions. Not much is known about the impact of strong many particle correlations on spin and valley polarization dynamics. Here we report direct measurements of ultrafast valley specific relaxation dynamics in single layer MoS2 and WS2. We found that excitonic many body interactions significantly contribute to the relaxation process. Biexciton formation reveals hole valley/spin relaxation time in MoS2. Our results suggest that initial fast intervalley electron scattering and electron spin relaxation leads to loss of valley polarization for holes through an electron-hole spin exchange mechanism in both MoS2 and WS2.}, booktitle={Ultrafast Nonlinear Imaging and Spectroscopy II}, publisher={SPIE}, author={Barrette, Andrew and Mai, Cong and Yu, Yifei and Semenov, Yuriy and Jin, Zhenghe and Kim, Ki Wook and Cao, Linyou and Gundogdu, Kenan}, editor={Liu, ZhiwenEditor}, year={2014}, month={Sep} }
 @article{semenov_duan_kim_2014, title={Voltage-driven magnetic bifurcations in nanomagnet–topological insulator heterostructures}, volume={89}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.89.201405}, DOI={10.1103/physrevb.89.201405}, abstractNote={Multiplicity of magnetization dynamics in a thin insulating ferromagnet deposited on a topological insulator (TI) is studied as a function of electron flow at the interface. The spin current of TI surface electrons induces magnetization precession in the magnet, which in turn modifies the TI spin polarization. In contrast to the conventional linear analysis, the self-consistent nature of the interaction leads to auto-oscillation, magnetization reversal, or magnetic deviation under a dc bias, all of which are accompanied by the strong anomalous Hall effect. With a minimal energy requirement as low as tens of aJ, the proposed mechanism offers a highly efficient alternative to the spin transfer torque or spin-Hall based approaches.Received 5 February 2014DOI:https://doi.org/10.1103/PhysRevB.89.201405©2014 American Physical Society}, number={20}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Duan, Xiaopeng and Kim, Ki Wook}, year={2014}, month={May} }
 @article{mao_kong_gong_xu_jayasekera_cho_kim_2013, title={First-principles calculation of thermal transport in metal/graphene systems}, volume={87}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.87.165410}, DOI={10.1103/physrevb.87.165410}, abstractNote={Thermal properties in the metal/graphene (Gr) systems are analyzed by using an atomistic phonon transport model based on Landauer formalism and first-principles calculations. The specific structures under investigation include chemisorbed Ni(111)/Gr, physisorbed Cu(111)/Gr and Au(111)/Gr, as well as Pd(111)/Gr with intermediate characteristics. Calculated results illustrate a strong dependence of thermal transfer on the details of interfacial microstructures. In particular, it is shown that the chemisorbed case provides a generally smaller interfacial thermal resistance than the physisorbed one due to the stronger bonding. However, our calculation also indicates that the weakly chemisorbed interface of Pd/Gr may be an exception, with the largest thermal resistance among the considered. Further examination of the electrostatic potential and interatomic force constants reveals that the mixed bonding force between the Pd and C atoms results in incomplete hybridization of Pd and graphene orbital states at the junction, leading effectively to two phonon interfaces and a larger than expected thermal resistance. Comparison with available experimental data shows good agreement. The result clearly suggests the feasibility of phonon engineering for thermal property optimization at the interface.}, number={16}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Mao, R. and Kong, B. D. and Gong, C. and Xu, S. and Jayasekera, T. and Cho, K. and Kim, K. W.}, year={2013}, month={Apr} }
 @article{li_mullen_jin_borysenko_buongiorno nardelli_kim_2013, title={Intrinsic electrical transport properties of monolayer silicene and MoS2from first principles}, volume={87}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.87.115418}, DOI={10.1103/physrevb.87.115418}, abstractNote={Article on intrinsic electrical transport properties of monolayer silicene and MoS₂ from first principles.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Li, Xiaodong and Mullen, Jeffrey T. and Jin, Zhenghe and Borysenko, Kostyantyn M. and Buongiorno Nardelli, M. and Kim, Ki Wook}, year={2013}, month={Mar} }
 @article{mai_barrette_yu_semenov_kim_cao_gundogdu_2013, title={Many-Body Effects in Valleytronics: Direct Measurement of Valley Lifetimes in Single-Layer MoS2}, volume={14}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl403742j}, DOI={10.1021/nl403742j}, abstractNote={Single layer MoS2 is an ideal material for the emerging field of "valleytronics" in which charge carrier momentum can be finely controlled by optical excitation. This system is also known to exhibit strong many-body interactions as observed by tightly bound excitons and trions. Here we report direct measurements of valley relaxation dynamics in single layer MoS2, by using ultrafast transient absorption spectroscopy. Our results show that strong Coulomb interactions significantly impact valley population dynamics. Initial excitation by circularly polarized light creates electron-hole pairs within the K-valley. These excitons coherently couple to dark intervalley excitonic states, which facilitate fast electron valley depolarization. Hole valley relaxation is delayed up to about 10 ps due to nondegeneracy of the valence band spin states. Intervalley biexciton formation reveals the hole valley relaxation dynamics. We observe that biexcitons form with more than an order of magnitude larger binding energy compared to conventional semiconductors. These measurements provide significant insight into valley specific processes in 2D semiconductors. Hence they could be used to suggest routes to design semiconducting materials that enable control of valley polarization.}, number={1}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Mai, Cong and Barrette, Andrew and Yu, Yifei and Semenov, Yuriy G. and Kim, Ki Wook and Cao, Linyou and Gundogdu, Kenan}, year={2013}, month={Dec}, pages={202–206} }
 @inproceedings{duan_semenov_kim_2013, title={Spin logic via controlled correlation in a topological insulator-nanomagnet hybrid structure}, ISBN={9781479908141 9781479908110 9781479908127}, url={http://dx.doi.org/10.1109/drc.2013.6633829}, DOI={10.1109/drc.2013.6633829}, abstractNote={A magnetic switching device implemented with a majority-gate logic structure is explored as a potential candidate for beyond-CMOS technology. Specifically, a novel switching mechanism is envisioned that relies on the unique magneto-electric properties of a hybrid structure consisting of topological insulator (TI), insulating ferromagnet (FM) and graphene (Gr) in the Bennett clocking operation scheme (Fig. 1A). A circuit layout is proposed and the logic operation demonstrated in a 1-bit adder.}, booktitle={71st Device Research Conference}, publisher={IEEE}, author={Duan, Xiaopeng and Semenov, Yuriy G and Kim, Ki Wook}, year={2013}, month={Jun} }
 @article{kong_trew_kim_2013, title={Toward stimulated interaction of surface phonon polaritons}, volume={114}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4851717}, DOI={10.1063/1.4851717}, abstractNote={Thermal emission spectra mediated by surface phonon polariton are examined by using a theoretical model that accounts for generation processes. Specifically, the acoustic phonon fusion mechanism is introduced to remedy theoretical deficiencies of the near thermal equilibrium treatments. The model clarifies the thermal excitation mechanism of surface phonon polaritons and the energy transfer path under non-zero energy flow. When applied to GaAs and SiC semi-infinite surfaces, the nonequilibrium model predicts that the temperature dependence of the quasi-monochromatic peak can exhibit distinctly different characteristics of either sharp increase or slow saturation depending on the materials, which is in direct contrast with the estimate made by the near-equilibrium model. The proposed theoretical tool can accurately analyze the nonequilibrium steady states, potentially paving a pathway to demonstrate stimulated interaction/emission of thermally excited surface phonon polaritons.}, number={23}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kong, B. D. and Trew, R. J. and Kim, K. W.}, year={2013}, month={Dec}, pages={233508} }
 @article{calzolari_jayasekera_kim_nardelli_2012, title={Ab initiothermal transport properties of nanostructures from density functional perturbation theory}, volume={24}, ISSN={0953-8984 1361-648X}, url={http://dx.doi.org/10.1088/0953-8984/24/49/492204}, DOI={10.1088/0953-8984/24/49/492204}, abstractNote={We present a comprehensive first-principles study of the thermal transport properties of low-dimensional nanostructures such as polymers and nanowires. An approach is introduced where the phonon quantum conductance is computed from the combination of accurate plane-wave density functional theory electronic structure calculations, the evaluation of the interatomic force constants through density functional perturbation theory for lattice dynamics, and the calculation of transport properties by a real-space Green’s function method based on the Landauer formalism. This approach is computationally very efficient, can be straightforwardly implemented as a post-processing step in a standard electronic structure calculation (Quantum ESPRESSO and WanT in the present implementation), and allows us to directly link the thermal transport properties of a device to the coupling, dimensionality, and atomistic structure of the system. It provides invaluable insight into the mechanisms that govern heat flow at the nanoscale and paves the way to the fundamental understanding of phonon engineering in nanostructures.}, number={49}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Calzolari, Arrigo and Jayasekera, Thushari and Kim, Ki Wook and Nardelli, Marco Buongiorno}, year={2012}, month={Nov}, pages={492204} }
 @article{sidorov_gaskill_buongiorno nardelli_tedesco_myers-ward_eddy_jayasekera_kim_jayasingha_sherehiy_et al._2012, title={Charge transfer equilibria in ambient-exposed epitaxial graphene on (0001¯) 6 H-SiC}, volume={111}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4725413}, DOI={10.1063/1.4725413}, abstractNote={The transport properties of electronic materials have been long interpreted independently from both the underlying bulk-like behavior of the substrate or the influence of ambient gases. This is no longer the case for ultra-thin graphene whose properties are dominated by the interfaces between the active material and its surroundings. Here, we show that the graphene interactions with its environments are critical for the electrostatic and electrochemical equilibrium of the active device layers and their transport properties. Based on the prototypical case of epitaxial graphene on (0001¯) 6 H-SiC and using a combination of in-situ thermoelectric power and resistance measurements and simulations from first principles, we demonstrate that the cooperative occurrence of an electrochemically mediated charge transfer from the graphene to air, combined with the peculiar electronic structure of the graphene/SiC interface, explains the wide variation of measured conductivity and charge carrier type found in prior reports.}, number={11}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Sidorov, Anton N. and Gaskill, Kurt and Buongiorno Nardelli, Marco and Tedesco, Joseph L. and Myers-Ward, Rachel L. and Eddy, Charles R., Jr. and Jayasekera, Thushari and Kim, Ki Wook and Jayasingha, Ruwantha and Sherehiy, Andriy and et al.}, year={2012}, month={Jun}, pages={113706} }
 @article{semenov_duan_kim_2012, title={Electrically controlled magnetization in ferromagnet-topological insulator heterostructures}, volume={86}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.86.161406}, DOI={10.1103/physrevb.86.161406}, abstractNote={An approach to the electrostatic control of $90^{\circ}$ magnetization rotation in the hybrid structures composed of topological insulators (TIs) and adjacent ferromagnetic insulators (FMI) is proposed and studied. The concept is based on TI electron energy variation with in-plane to put-of plane FMI magnetization turn. The calculations explicitly expose the effect of free energy variability in the form of the electrically controlled uniaxial magnetic anisotropy, which depends on proximate exchange interaction and TI surface electron density. Combining with inherent anisotropy, the magnetization rotation from in-plane to out-of-plane direction is shown to be realizable for 1.7~2.7 ns under the electrical variation of TI chemical potential in the range $\pm$ 100 meV around Dirac point. When bias is withdrawn a small signal current can target the out-of-plane magnetization instable state to the desirable direction of in-plane easy axis, thus the structure can lay the foundation for low energy nonvolatile memory prototype.}, number={16}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Duan, Xiaopeng and Kim, Ki Wook}, year={2012}, month={Oct} }
 @article{jayasekera_kim_nardelli_2012, title={Electronic and Structural Properties of Turbostratic Epitaxial Graphene on the 6H-SiC (000-1) Surface}, volume={717-720}, ISSN={1662-9752}, url={http://dx.doi.org/10.4028/www.scientific.net/MSF.717-720.595}, DOI={10.4028/www.scientific.net/MSF.717-720.595}, abstractNote={We propose an atomistic model to study the interface properties of mis-oriented (turbostratic) epitaxial graphene on SiC (000-1) surface. Using calculations from first principles, we compare the energetics, and structural/electronic properties of AB and turbostratic stacking sequences within a model based on the Si adatom surface reconstruction. Our calculations show that the systems with AB and turbostratic sequences are very close in energy, demonstrating the possibility of the observation of Moire patterns in epitaxial graphene on the C-face of SiC. The two-dimensional electron gas behavior is preserved in the epitaxial turbostratic graphene systems. However, there are deviations from the ideal turbostratic epitaxial graphene.}, journal={Materials Science Forum}, publisher={Trans Tech Publications}, author={Jayasekera, Thushari and Kim, K.W. and Nardelli, M. Buongiorno}, year={2012}, month={May}, pages={595–600} }
 @article{duan_stephanovich_semenov_kim_2012, title={Magnetic domain wall transfer via graphene mediated electrostatic control}, volume={101}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4732794}, DOI={10.1063/1.4732794}, abstractNote={A mechanism that enables electrically controlled magnetic domain wall transfer in a ferromagnetic insulator (FMI) is investigated theoretically by utilizing graphene as a crucial mediating material. The concept is grounded on the variability of the exchange interaction energy between a ferromagnetic insulator and a proximate graphene layer with an inhomogeneous carrier density. A memory device prototype is proposed based on the effect that does not require an active current for its intrinsic function. Our analysis illustrates the highly efficient device operation, with an estimated switching energy of 10−16 J for one binary bit of nonvolatile information.}, number={1}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Duan, X. and Stephanovich, V. A. and Semenov, Y. G. and Kim, K. W.}, year={2012}, month={Jul}, pages={013103} }
 @article{sandin_jayasekera_rowe_kim_buongiorno nardelli_dougherty_2012, title={Multiple coexisting intercalation structures of sodium in epitaxial graphene-SiC interfaces}, volume={85}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.85.125410}, DOI={10.1103/physrevb.85.125410}, abstractNote={This article discusses multiple coexisting intercalation structures of sodium in peitaxial graphene-SiC interfaces.}, number={12}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Sandin, Andreas and Jayasekera, Thushari and Rowe, J. E. and Kim, Ki Wook and Buongiorno Nardelli, M. and Dougherty, Daniel B.}, year={2012}, month={Mar} }
 @article{mao_kong_kim_jayasekera_calzolari_buongiorno nardelli_2012, title={Phonon engineering in nanostructures: Controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions}, volume={101}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4752437}, DOI={10.1063/1.4752437}, abstractNote={Article discussing phonon engineering in nanostructures and controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Mao, R. and Kong, B. D. and Kim, K. W. and Jayasekera, T. and Calzolari, A. and Buongiorno Nardelli, M.}, year={2012}, month={Sep}, pages={113111} }
 @article{sidorov_gaskill_buongiorno nardelli_tedesco_myers-ward_eddy_jayasekera_wook kim_jayasingha_sherehiy_et al._2012, title={Publisher’s Note: “Charge transfer equilibria in ambient-exposed epitaxial graphene on (0001¯) 6 H-SiC” [J. Appl. Phys. 111, 113706 (2012)]}, volume={112}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.4742134}, DOI={10.1063/1.4742134}, abstractNote={First Page}, number={2}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Sidorov, Anton N. and Gaskill, Kurt and Buongiorno Nardelli, Marco and Tedesco, Joseph L. and Myers-Ward, Rachel L. and Eddy, Charles R., Jr. and Jayasekera, Thushari and Wook Kim, Ki and Jayasingha, Ruwantha and Sherehiy, Andriy and et al.}, year={2012}, month={Jul}, pages={029908} }
 @article{semenov_li_kim_2012, title={Tunable photogalvanic effect on topological insulator surfaces via proximity interactions}, volume={86}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.86.201401}, DOI={10.1103/physrevb.86.201401}, abstractNote={An unusual photo-galvanic effect is predicted on the topological insulator surface when its semi-metallic electronic spectrum is modified by an adjacent ferromagnet. The effect is correlated with light absorption in a wide frequency range (from a few to hundreds of meV) and produces a pronounced response that is not only resonant to the photon energy but also tunable by an external electrical bias. The exceptionally strong peak photocurrent of the order of $\mu$A/cm may be achieved at elevated temperatures with the illumination power of 1 W/cm$^2$ in the THz range on Bi$_2$Se$_3$. These advantages could enable room-temperature detection of far-infrared radiation.}, number={20}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Yuriy G. and Li, Xiaodong and Kim, Ki Wook}, year={2012}, month={Nov} }
 @article{kong_zeng_gaskill_wang_kim_2012, title={Two dimensional crystal tunneling devices for THz operation}, volume={101}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.4773514}, DOI={10.1063/1.4773514}, abstractNote={Two dimensional crystal heterostructures are shown to possess a unique opportunity for nonlinear THz devices. In contrast to the oxide tunneling barrier, the uniformity of layered crystal insulators provides an ideal condition for tunneling barriers in the atomic scale. Numerical calculations based on a first-principles method clearly indicate the feasibility of diode operation with barriers as thin as two monolayers when placed between graphene-metal asymmetric electrodes. Further analysis predicts cut-off frequencies over 10 THz while maintaining strong nonlinearity for zero-bias rectification. Application to hot electron transistors is also examined, illustrating potentially superior performance in the frequency range inaccessible thus far.}, number={26}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kong, B. D. and Zeng, C. and Gaskill, D. K. and Wang, K. L. and Kim, K. W.}, year={2012}, month={Dec}, pages={263112} }
 @article{korotyeyev_kochelap_kim_2011, title={Electron transport in bulk GaN under ultrashort high-electric field transient}, volume={26}, ISSN={0268-1242 1361-6641}, url={http://dx.doi.org/10.1088/0268-1242/26/10/105008}, DOI={10.1088/0268-1242/26/10/105008}, abstractNote={We have investigated nonlinear electron transport in GaN induced by high-electric field transients by analyzing the temporal dependence of the electron drift velocity and temperature. For picosecond transients, our calculations have established that the electron dynamics retain almost all the features of the steady-state velocity-field characteristics including the portion with negative differential conductivity. It was also found that transient currents in GaN samples give rise to the THz re-emission effect—radiation of electromagnetic field, temporal and spectral properties of which directly relate to the velocity-field characteristics of the sample. The results clearly indicate that existing methods for the generation of high-electric field transients and subpicosecond signal measurements can be applied to the characterization of hot electron transport at ultrahigh fields while avoiding Joule self-heating, hot phonon accumulation and other undesirable effects.}, number={10}, journal={Semiconductor Science and Technology}, publisher={IOP Publishing}, author={Korotyeyev, V V and Kochelap, V A and Kim, K W}, year={2011}, month={Sep}, pages={105008} }
 @article{li_borysenko_nardelli_kim_2011, title={Electron transport properties of bilayer graphene}, volume={84}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.84.195453}, DOI={10.1103/physrevb.84.195453}, abstractNote={Electron transport in bilayer graphene is studied by using a first principles analysis and theMonte Carlo simulation under conditions relevant to potential applications. While the intrinsic properties are found to be much less desirable in bilayer than in monolayer graphene, with significantly reduced mobilities and saturation velocities, the calculation also reveals the dominant influence of extrinsic factors such as the substrate and impurities. Accordingly, the difference between two graphene forms are more muted in realistic settings although the velocity-field characteristics remain substantially lower in the bilayer. When bilayer graphene is subject to an interlayer bias, the resulting changes in the energy dispersion lead to stronger electron scattering at the bottom of the conduction band. The mobility decreases significantly with the size of the generated bandgap, whereas the saturation velocity remains largely unaffected.}, number={19}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Li, X. and Borysenko, K. M. and Nardelli, M. Buongiorno and Kim, K. W.}, year={2011}, month={Nov} }
 @article{borysenko_mullen_li_semenov_zavada_nardelli_kim_2011, title={Electron-phonon interactions in bilayer graphene}, volume={83}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.83.161402}, DOI={10.1103/physrevb.83.161402}, abstractNote={K. M. Borysenko, J. T. Mullen, X. Li, Y. G. Semenov, J. M. Zavada, M. Buongiorno Nardelli, 3 and K. W. Kim Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7911 Department of Physics, North Carolina State University, Raleigh, NC 27695-8202 CSMD, Oak Ridge National Laboratory, Oak Ridge, TN 37831 Abstract Using calculations from first principles, we demonstrate that intrinsic carrier-phonon scattering in bilayer graphene is dominated by low energy acoustic (and acoustic-like) phonon modes in a framework that bears more resemblance with bulk graphite than monolayer graphene. The total scattering rate at low/moderate electron energies can be described by a simple two-phonon model in the deformation potential approximation with effective constants Dac ≈ 15 eV and Dop ≈ 2.8 × 108 eV/cm for acoustic and optical phonons, respectively. With much enhanced acoustic phonon scattering, the low field mobility of intrinsic bilayer graphene is estimated to be significantly smaller than that of the monolayer: μ = 8.4× 104 cm2/V·s}, number={16}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Borysenko, K. M. and Mullen, J. T. and Li, X. and Semenov, Y. G. and Zavada, J. M. and Nardelli, M. Buongiorno and Kim, K. W.}, year={2011}, month={Apr} }
 @article{jayasekera_xu_kim_nardelli_2011, title={Electronic properties of the graphene/6H-SiC(0001¯) interface: A first-principles study}, volume={84}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.84.035442}, DOI={10.1103/physrevb.84.035442}, abstractNote={Using calculations from first principles, we show how the structural and electronic properties of epitaxial graphene on 6H-SiC(0001) are determined by the geometry and the chemical functionalization of the interface region. We also demonstrate that these properties can be correctly captured only if a proper treatment of the van der Waals interactions is included in the theoretical description based on density functional theory. Our results reproduce the experimentally observed n-type doping of monolayer epitaxial graphene and prove the possibility of opening a sizable (150 meV) energy gap in the bilayer case under special growth conditions. Depending on the details of the bonding at the interface, we are able to interpret recent experimental observations and provide a clear insight into the mechanisms of charge transfer and interface stability.}, number={3}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Jayasekera, Thushari and Xu, Shu and Kim, K. W. and Nardelli, M. Buongiorno}, year={2011}, month={Jul} }
 @article{sokolov_kochelap_kim_2011, title={Generation-recombination noise in bipolar graphene}, volume={110}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3626820}, DOI={10.1063/1.3626820}, abstractNote={A theoretical model is developed for the intrinsic generation-recombination (G-R) noise in bipolar graphene that stems from stochastic processes of interband carrier transitions in the zero-gap single layer. The correlation functions are obtained for microscopic Langevin sources of fluctuations relevant to the considered G-R processes. The spectral density of the G-R fluctuations is of a Lorentz shape with the characteristic frequency fc=1/2πτr, where the recombination time τr is expressed through the G-R rates and the carrier density. Numerical estimates clearly demonstrate the potential dominance of G-R noise over the Nyquist and flicker noise in monolayer graphene.}, number={4}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Sokolov, V. N. and Kochelap, V. A. and Kim, K. W.}, year={2011}, month={Aug}, pages={044327} }
 @article{li_kong_zavada_kim_2011, title={Strong substrate effects of Joule heating in graphene electronics}, volume={99}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3668113}, DOI={10.1063/1.3668113}, abstractNote={The effect of Joule heating on graphene electronic properties is investigated by self-consistent use of full-band Monte Carlo electron dynamics and three-dimensional heat transfer simulations. Several technologically important substrate materials are examined: SiO2, SiC, hexagonal BN, and diamond. Results illustrate that the choice of substrate has a major impact via heat conduction and surface polar phonon scattering. Particularly, the poor thermal conductivity of SiO2 leads to significant Joule heating and saturation velocity degradation in graphene characterized by the 1/n decay. Considering the overall characteristics, BN appears to compare favorably against the other substrate choices for graphene electronic applications.}, number={23}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Li, X. and Kong, B. D. and Zavada, J. M. and Kim, K. W.}, year={2011}, month={Dec}, pages={233114} }
 @article{kong_semenov_krowne_kim_2011, title={Unusual magnetoresistance in a topological insulator with a single ferromagnetic barrier}, volume={98}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3600330}, DOI={10.1063/1.3600330}, abstractNote={Tunneling surface current through a thin ferromagnetic barrier on a three-dimensional topological insulator is shown to possess an extraordinary response to the orientation of barrier magnetization. In contrast to conventional magnetoresistance devices that are sensitive to the relative alignment of two magnetic layers, a drastic change in the transmission current is achieved by a single layer when its magnetization rotates by 90°. Numerical estimations predict a giant magnetoresistance as large as 800% at room temperature with the proximate exchange energy of 40 meV at the barrier interface. When coupled with electrical control of magnetization direction, this phenomenon may be used to enhance the gating function with potentially sharp turn-on/off for low power applications.}, number={24}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kong, B. D. and Semenov, Y. G. and Krowne, C. M. and Kim, K. W.}, year={2011}, month={Jun}, pages={243112} }
 @article{semenov_zavada_kim_2011, title={Weak ferromagnetism of antiferromagnetic domains in graphene with defects}, volume={84}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.84.165435}, DOI={10.1103/physrevb.84.165435}, abstractNote={Magnetic properties of graphene with randomly distributed magnetic defects/vacancies are studied in terms of the Kondo Hamiltonian in the mean field approximation. It has been shown that graphene with defects undergoes a magnetic phase transition from a paramagnetic to a antiferromagnetic (AFM) phase once the temperature reaches the critical point $T_{N}$. The defect straggling is taken into account as an assignable cause of multiple nucleation into AFM domains. Since each domain is characterized by partial compensating magnetization of the defects associated with different sublattices, together they reveal a super-paramagnetic behavior in a magnetic field. Theory qualitatively describe the experimental data provided the temperature dependence of the AFM domain structure.}, number={16}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2011}, month={Oct} }
 @article{jayasekera_kong_kim_buongiorno nardelli_2010, title={Band Engineering and Magnetic Doping of Epitaxial Graphene on SiC (0001)}, volume={104}, ISSN={0031-9007 1079-7114}, url={http://dx.doi.org/10.1103/PhysRevLett.104.146801}, DOI={10.1103/physrevlett.104.146801}, abstractNote={Using calculations from first principles we show how specific interface modifications can lead to a fine-tuning of the doping and band alignment in epitaxial graphene on SiC. Upon different choices of dopants, we demonstrate that one can achieve a variation of the valence band offset between the graphene Dirac point and the valence band edge of SiC up to 1.5 eV. Finally, via appropriate magnetic doping one can induce a half-metallic behavior in the first graphene monolayer. These results clearly establish the potential for graphene utilization in innovative electronic and spintronic devices.}, number={14}, journal={Physical Review Letters}, publisher={American Physical Society (APS)}, author={Jayasekera, Thushari and Kong, B. D. and Kim, K. W. and Buongiorno Nardelli, M.}, year={2010}, month={Apr} }
 @article{semenov_zavada_kim_2010, title={Electrically controlled magnetic switching based on graphene-magnet composite structures}, volume={107}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3354066}, DOI={10.1063/1.3354066}, abstractNote={A nonvolatile magnetic switch is proposed by utilizing the unique properties of graphene-ferromagnet composite structures. The basic mechanism relies on the role of graphene in mediating and modulating the effective exchange bias between adjacent magnetic layers, which can lead to electrically controlled rotation of magnetic bits. Readout of magnetization states is also achieved electrically through the magnetoresistance effect in the graphene channel. The proposed switch can be used to realize both the memory and programmable logic elements. Theoretical estimates illustrate the feasibility of the concept as well as its potential advantage of low power consumption (∼10−19 J) for the intrinsic switching operation.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2010}, month={Mar}, pages={064507} }
 @article{semenov_zavada_kim_2010, title={Electron spin relaxation in carbon nanotubes}, volume={82}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.82.155449}, DOI={10.1103/physrevb.82.155449}, abstractNote={The long standing problem of inexplicably short spin relaxation in carbon nanotubes (CNTs) is examined. The curvature-mediated spin-orbital interaction is shown to induce fluctuating electron spin precession causing efficient relaxation in a manner analogous to the Dyakonov-Perel mechanism. Our calculation estimates longitudinal (spin-flip) and transversal (decoherence) relaxation times as short as 150 ps and 110 ps at room temperature, respectively, along with a pronounced anisotropic dependence. Interference of electrons originating from different valleys can lead to even faster dephasing. The results can help clarify the measured data, resolving discrepancies in the literature.}, number={15}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2010}, month={Oct} }
 @article{borysenko_mullen_barry_paul_semenov_zavada_nardelli_kim_2010, title={First-principles analysis of electron-phonon interactions in graphene}, volume={81}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.81.121412}, DOI={10.1103/physrevb.81.121412}, abstractNote={The electron-phonon interaction in monolayer graphene is investigated using density-functional perturbation theory. The results indicate that the electron-phonon interaction strength is of comparable magnitude for all four in-plane phonon branches and must be considered simultaneously. Moreover, the calculated scattering rates suggest an acoustic-phonon contribution that is much weaker than previously thought, revealing an important role of optical phonons even at low energies. Accordingly it is predicted, in good agreement with a recent measurement, that the intrinsic mobility of graphene may be more than an order of magnitude larger than the already high values reported in suspended samples.}, number={12}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Borysenko, K. M. and Mullen, J. T. and Barry, E. A. and Paul, S. and Semenov, Y. G. and Zavada, J. M. and Nardelli, M. Buongiorno and Kim, K. W.}, year={2010}, month={Mar} }
 @article{semenov_zavada_kim_2010, title={Graphene spin capacitor for magnetic field sensing}, volume={97}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3462297}, DOI={10.1063/1.3462297}, abstractNote={An analysis of a magnetic field sensor based on a graphene spin capacitor is presented. The proposed device consists of graphene nanoribbons on top of an insulator material connected to a ferromagnetic source/drain. The time evolution of spin polarized electrons injected into the capacitor can be used for an accurate determination at room temperature of external magnetic fields. Assuming a spin relaxation time of 100 ns, magnetic fields on the order of ∼10 mOe may be detected at room temperature. The observational accuracy of this device depends on the density of magnetic defects and spin relaxation time that can be achieved.}, number={1}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2010}, month={Jul}, pages={013106} }
 @article{li_barry_zavada_nardelli_kim_2010, title={Influence of electron-electron scattering on transport characteristics in monolayer graphene}, volume={97}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3483612}, DOI={10.1063/1.3483612}, abstractNote={The influence of electron-electron scattering on the distribution function and transport characteristics of intrinsic monolayer graphene is investigated via an ensemble Monte Carlo simulation. Due to the linear dispersion relation in the vicinity of the Dirac points, it is found that pair-wise collisions in graphene do not conserve the ensemble average velocity in contrast to conventional semiconductors with parabolic energy bands. Numerical results indicate that electron-electron scattering can lead to a decrease in the low field mobility by more than a factor of 2 for moderate electron densities. The corresponding degradation in the saturation velocity is more modest at around 15%. At high densities, the impact gradually diminishes due to increased degeneracy.}, number={8}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Li, X. and Barry, E. A. and Zavada, J. M. and Nardelli, M. Buongiorno and Kim, K. W.}, year={2010}, month={Aug}, pages={082101} }
 @article{barry_sokolov_kim_trew_2010, title={Large-Signal Analysis of Terahertz Generation in Submicrometer GaN Diodes}, volume={10}, ISSN={1530-437X 1558-1748}, url={http://dx.doi.org/10.1109/JSEN.2009.2038132}, DOI={10.1109/jsen.2009.2038132}, abstractNote={The conditions for microwave power generation in a submicrometer GaN diode, with a relatively lightly doped active channel, coupled to an external resonant circuit are investigated. Applying a high-field electron transport model based on the local quasi-static approximation, we show that oscillations in group III-nitride diodes can be supported in the terahertz-frequency range near the limited space-charge accumulation regime. The shape of the diode voltage and electronic current waveforms are examined in terms of the circuit parameters and operating frequencies over the bandwidth of active generation. Based on a Fourier series analysis of the diode voltage and current, the generated power and dc-to-RF conversion efficiency at the fundamental and the second or higher order harmonic frequencies are estimated. The calculation results clearly indicate that submicrometer GaN diodes (channel doping of 1 × 1017 cm-3) can achieve large output powers (> 1 W) in the absence of Gunn domain formation, over a wide range of frequencies, near 0.5 THz.}, number={3}, journal={IEEE Sensors Journal}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Barry, E. A. and Sokolov, V. N. and Kim, K. W. and Trew, R. J.}, year={2010}, month={Mar}, pages={765–771} }
 @article{sokolov_kochelap_kim_2010, title={Magnetoconcentration effect in intrinsic graphene ribbons}, volume={97}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3486124}, DOI={10.1063/1.3486124}, abstractNote={We consider transverse redistributions of the electrons and holes in intrinsic graphene ribbons under the influence of crossed electric and magnetic fields, i.e., the magnetoconcentration effect. The electron and hole transport is described from the Boltzmann kinetic equation assuming the local quasiequilibrium distributions of the carriers over energy states. The effective control of the carriers is achieved from deep depletion to accumulation modes depending on the properties of the ribbon edges, provided electron-hole recombination/generation rates at the edges are different from those inside the ribbon. The current-voltage characteristics reflect the behavior of the carrier redistributions across the ribbon. The obtained results suggest that interesting effects such as the population inversion in certain ranges of energies and the induced transparency are possible, which make them attractive for various optoelectronics applications in the terahertz spectral range.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Sokolov, V. N. and Kochelap, V. A. and Kim, K. W.}, year={2010}, month={Sep}, pages={112112} }
 @article{kong_sokolov_kim_trew_2010, title={Quasi-Coherent Thermal Emission in the Terahertz by Doped Semiconductors}, volume={10}, ISSN={1530-437X 1558-1748}, url={http://dx.doi.org/10.1109/JSEN.2009.2038133}, DOI={10.1109/jsen.2009.2038133}, abstractNote={We investigate thermal emission characteristics mediated by surface plasmon polaritons (SPPs) resonantly excited at a semiconductor-vacuum interface. The characteristic plasma and SPP resonant frequencies in the interval from 0.3 to 10 THz can be controlled with conventional doping densities. All of the cases under consideration (n-doped GaAs, GaN, and Si) demonstrate the spectral energy density in the near field that is several orders of magnitude larger than the blackbody radiation. The strongly resonant SPPs are also shown to enhance drastically the radiative heat transfer between two semi-infinite surfaces separated by nanometric distances. The possibility of extending spatially coherent emission through 1-D binary grating is examined based on a rigorous coupled-wave analysis. Our calculation results clearly indicate that n-doped semiconductors with properly designed surface grating can achieve efficient directional thermal emission in the THz frequency range for potential use in a number of applications including sensing.}, number={3}, journal={IEEE Sensors Journal}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Kong, B. D. and Sokolov, V. N. and Kim, K. W. and Trew, R. J.}, year={2010}, month={Mar}, pages={443–450} }
 @article{li_barry_zavada_buongiorno nardelli_kim_2010, title={Surface polar phonon dominated electron transport in graphene}, volume={97}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3525606}, DOI={10.1063/1.3525606}, abstractNote={The effects of surface polar phonons on the electronic transport properties of monolayer graphene are studied by using a Monte Carlo simulation. Specifically, the low-field electron mobility and saturation velocity are examined for different substrates (SiC, SiO2, and HfO2) in comparison to the intrinsic case. While the results show that the low-field mobility can be substantially reduced by the introduction of surface polar phonon scattering, corresponding degradation of the saturation velocity is not observed for all three substrates at room temperature. It is also found that surface polar phonons can influence graphene’s electrical resistivity even at low temperature, leading potentially to inaccurate estimation of the acoustic phonon deformation potential constant.}, number={23}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Li, X. and Barry, E. A. and Zavada, J. M. and Buongiorno Nardelli, M. and Kim, K. W.}, year={2010}, month={Dec}, pages={232105} }
 @article{chen_jayasekera_calzolari_kim_buongiorno nardelli_2010, title={Thermoelectric properties of graphene nanoribbons, junctions and superlattices}, volume={22}, ISSN={0953-8984 1361-648X}, url={http://dx.doi.org/10.1088/0953-8984/22/37/372202}, DOI={10.1088/0953-8984/22/37/372202}, abstractNote={Using model interaction Hamiltonians for both electrons and phonons and Green’s function formalism for ballistic transport, we have studied the thermal conductance and the thermoelectric properties of graphene nanoribbons (GNR), GNR junctions and periodic superlattices. Among our findings we have established the role that interfaces play in determining the thermoelectric response of GNR systems both across single junctions and in periodic superlattices. In general, increasing the number of interfaces in a single GNR system increases the peak ZT values that are thus maximized in a periodic superlattice. Moreover, we proved that the thermoelectric behavior is largely controlled by the width of the narrower component of the junction. Finally, we have demonstrated that chevron-type GNRs recently synthesized should display superior thermoelectric properties.}, number={37}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Chen, Y and Jayasekera, T and Calzolari, A and Kim, K W and Buongiorno Nardelli, M}, year={2010}, month={Aug}, pages={372202} }
 @article{galatsis_khitun_ostroumov_wang_dichtel_plummer_stoddart_zink_lee_xie_et al._2009, title={Alternate State Variables for Emerging Nanoelectronic Devices}, volume={8}, ISSN={1536-125X 1941-0085}, url={http://dx.doi.org/10.1109/TNANO.2008.2005525}, DOI={10.1109/TNANO.2008.2005525}, abstractNote={We provide an outlook of some important state variables for emerging nanoelectronic devices. State variables are physical representations of information used to perform information processing via memory and logic functionality. Advances in material science, emerging nanodevices, nanostructures, and architectures have provided hope that alternative state variables based on new mechanisms, nanomaterials, and nanodevices may indeed be plausible. We review and analyze the computational advantages that alternate state variables may possibly attain with respect to maximizing computational performance via minimum energy dissipation, maximum operating switching speed, and maximum device density.}, number={1}, journal={IEEE Transactions on Nanotechnology}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Galatsis, K. and Khitun, A. and Ostroumov, R. and Wang, K.L. and Dichtel, W.R. and Plummer, E. and Stoddart, J.F. and Zink, J.I. and Lee, Jae Young and Xie, Ya-Hong and et al.}, year={2009}, month={Jan}, pages={66–75} }
 @article{kong_paul_nardelli_kim_2009, title={First-principles analysis of lattice thermal conductivity in monolayer and bilayer graphene}, volume={80}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.80.033406}, DOI={10.1103/physrevb.80.033406}, abstractNote={Article on first-principles analysis of lattice thermal conductivity in monolayer and bilayer graphene.}, number={3}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kong, B. D. and Paul, S. and Nardelli, M. Buongiorno and Kim, K. W.}, year={2009}, month={Jul} }
 @article{barry_sokolov_kim_trew_2009, title={Terahertz generation in GaN diodes operating in pulsed regime limited by self-heating}, volume={94}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.3147217}, DOI={10.1063/1.3147217}, abstractNote={The conditions for pulsed regime operation of terahertz power generation in vertical nanoscale GaN-based diodes are investigated via self-consistent simulation of the high-field electron transport in the active channel and thermal transport in the entire device structure. The combined electrothermal model allows for a detailed analysis of the dynamical local distributions of the electric field, drift-velocity, and lattice temperature. We show that stable generation is achievable with a self-heating limited output power of 2.25 W at an operation frequency of 0.71 THz for a pulse width of 3 ns with a few tens of nanosecond duty cycle.}, number={22}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Barry, E. A. and Sokolov, V. N. and Kim, K. W. and Trew, R. J.}, year={2009}, month={Jun}, pages={222106} }
 @article{semenov_zavada_kim_2008, title={Electrical Control of Exchange Bias Mediated by Graphene}, volume={101}, ISSN={0031-9007 1079-7114}, url={http://dx.doi.org/10.1103/PhysRevLett.101.147206}, DOI={10.1103/physrevlett.101.147206}, abstractNote={The role of graphene in mediating the exchange interaction is theoretically investigated when placed between two ferromagnetic dielectric materials. The calculation based on a tight-binding model illustrates that the magnetic interactions at the interfaces affect not only the graphene band structure but also the thermodynamic potential of the system, leading to an effective exchange bias between magnetic layers. The analysis indicates a strong dependence of the exchange bias on the properties of the mediating layer, revealing an efficient mechanism of electrical control even at room temperature.}, number={14}, journal={Physical Review Letters}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2008}, month={Oct} }
 @article{borysenko_semenov_kim_zavada_2008, title={Electron spin relaxation via flexural phonon modes in semiconducting carbon nanotubes}, volume={77}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.77.205402}, DOI={10.1103/physrevb.77.205402}, abstractNote={This work considers the $g$-tensor anisotropy induced by the flexural thermal vibrations in one-dimensional structures and its role on electron spin relaxation. In particular, the mechanism of spin-lattice relaxation via flexural modes is theoretically studied for localized and delocalized electronic states in semiconducting carbon nanotubes in the presence of a magnetic field. The calculation of a one-phonon spin-flip process predicts distinctive dependencies of the relaxation rate on temperature, magnetic field, and nanotube diameter. A comparison to the spin relaxation caused by the hyperfine interaction clearly suggests the relative efficiency of the proposed mechanism at sufficiently high temperatures. Specifically, the longitudinal spin relaxation time in the semiconducting carbon nanotubes is estimated to be as short as $30\text{ }\ensuremath{\mu}\text{s}$ at room temperature.}, number={20}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Borysenko, K. M. and Semenov, Y. G. and Kim, K. W. and Zavada, J. M.}, year={2008}, month={May} }
 @article{enaya_semenov_zavada_kim_2008, title={Magnetic polaron for a spin memory application}, volume={104}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.3000482}, DOI={10.1063/1.3000482}, abstractNote={A memory concept based on the interfacial exchange energy between itinerant holes in a quantum dot and magnetic ions in an adjacent magnetic insulator is theoretically investigated. A model based on the free energy analysis demonstrates the existence of bistable states through the mechanism of bound collective magnetic polaron, whose formation and dissolution can be controlled electrically via a gate bias pulse. The parameter window suitable for bistability is discussed along with the conditions that support maximum nonvolatility. The analysis is extended to the influence of material choices as well as different designs. The calculation results clearly indicate the possibility of room temperature operation, given the availability of insulating ferromagnetic or antiferromagnetic materials whose Curie temperature is above room temperature.}, number={8}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Enaya, H. and Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2008}, month={Oct}, pages={084306} }
 @article{semenov_zavada_kim_2008, title={Magnetoresistance in bilayer graphene via ferromagnet proximity effects}, volume={77}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.77.235415}, DOI={10.1103/physrevb.77.235415}, abstractNote={A drastic modification of electronic band structure is predicted in bilayer graphene when it is placed between two ferromagnetic insulators. Due to the exchange interaction with the proximate ferromagnet, the electronic energy dispersion in the graphene channel strongly depends on the magnetization orientation of two ferromagnetic layers, $\mathbf{M_{1}}$ and $\mathbf{M_{2}} $. While the parallel configuration $\mathbf{M_{1}}= \mathbf{M_{2}}$ leads to simple spin splitting of both conduction and valence bands, an energy gap is induced as soon as the angle $\theta$ between $\mathbf{M_{1}}$ and $% \mathbf{M_{2}}$ becomes non-zero with the maximum achieved at $\theta=\pi$ (i.e., antiparallel alignment). Consequently, bilayer graphene may exhibit a sizable magnetoresistive effect in the current-in-plane configuration. A rough estimate suggests the resistance changes on the order of tens of percent at room temperature. This effect is expected to become more pronounced as the temperatures decreases.}, number={23}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Zavada, J. M. and Kim, K. W.}, year={2008}, month={Jun} }
 @article{enaya_semenov_kim_zavada_2008, title={Nonvolatile Memory via Spin Polaron Formation}, volume={7}, ISSN={1536-125X 1941-0085}, url={http://dx.doi.org/10.1109/TNANO.2008.926332}, DOI={10.1109/TNANO.2008.926332}, abstractNote={A nonvolatile memory is explored theoretically by utilizing the magnetic exchange interaction between localized holes and an adjacent ferromagnetic (FM) material. The active device consists of a buried semiconductor quantum dot (QD) and an FM insulating layer that share an interface. The hole population in the QD is controlled by particle transfer with a reservoir of itinerant holes over a permeable barrier. A theoretical model based on the free energy calculation demonstrates the existence of a bistable state through the mechanism of a collective spin polaron, whose formation and dissolution can be manipulated electrically via a gate bias pulse. The parameter space window suitable for bistability is examined along with the conditions that support maximum nonvolatility. The limitation of QD size scaling is analyzed in terms of the bit retention time.}, number={4}, journal={IEEE Transactions on Nanotechnology}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Enaya, H. and Semenov, Y.G. and Kim, K.W. and Zavada, J.M.}, year={2008}, month={Jul}, pages={480–483} }
 @inproceedings{kochelap_klimov_korotyeyev_kim_2008, title={Optical phonon instability caused by ultra-high-speed electron transport in nanoscale samples}, ISBN={9781424419739}, url={http://dx.doi.org/10.1109/CAOL.2008.4671902}, DOI={10.1109/CAOL.2008.4671902}, abstractNote={We investigated ultra-high frequency electrical properties of nanoscale n+-i-n+ diodes made of polar semiconductors. We found the optical vibrations instability and the large effect of the negative dynamic resistance. These effects indicate that the nanoscale diodes are capable of generating electromagnetic radiation in the 10 THz range.}, booktitle={2008 4th International Conference on Advanced Optoelectronics and Lasers}, publisher={IEEE}, author={Kochelap, V.A. and Klimov, A.A. and Korotyeyev, V.V. and Kim, K.W.}, year={2008}, month={Sep} }
 @article{kong_sokolov_kim_trew_2008, title={Terahertz emission mediated by surface plasmon polaritons in doped semiconductors with surface grating}, volume={103}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2840063}, DOI={10.1063/1.2840063}, abstractNote={Doped semiconductors with one-dimensional surface gratings are studied theoretically for application to terahertz emission. The presence of free carriers supports thermally excited surface plasmon polaritons at the semiconductor-vacuum interface whose resonance frequency can be controlled by doping. The calculation based on the fluctuational electrodynamics shows that the near-field spectral energy density of this surface excitation can be many orders of magnitude larger than those in the blackbody radiation. At the same time, a rigorous coupled-wave analysis with a properly designed surface microstructure clearly indicates narrow angular lobes in the directional emissivity at the targeted frequencies, illustrating strong coupling between surface plasmon polaritons and propagating waves. Thus, doped semiconductors with engineered radiation may provide an efficient terahertz source with spatial and spectral control.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kong, B. D. and Sokolov, V. N. and Kim, K. W. and Trew, R. J.}, year={2008}, month={Mar}, pages={056101} }
 @article{barry_sokolov_kim_trew_2008, title={Terahertz generation in GaN diodes in the limited space-charge accumulation mode}, volume={103}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2946717}, DOI={10.1063/1.2946717}, abstractNote={The conditions for terahertz power generation are investigated theoretically in a nanoscale GaN-based diode coupled to an external resonant circuit for operation in the limited space-charge accumulation (LSA) mode under the high-field transport regime. The generation criteria are revisited in terms of a phase plane analysis of the diode high-field transport and circuit equations. Based on a Fourier series analysis, the waveforms of the diode voltage and current are examined and the generated power and conversion efficiencies are estimated at the fundamental and lowest harmonic frequencies. The advantages of group-III nitride LSA diodes are elucidated including their ability to simultaneously achieve large output powers (>10 mW) and high dc-to-rf conversion efficiencies (>1%) over a wide range of frequencies near 1 THz.}, number={12}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Barry, E. A. and Sokolov, V. N. and Kim, K. W. and Trew, R. J.}, year={2008}, month={Jun}, pages={126101} }
 @inproceedings{enaya_semenov_kim_zavada_2007, title={A quantum dot memory cell based on spin polaron formation}, ISBN={9781424418916 9781424418923}, url={http://dx.doi.org/10.1109/isdrs.2007.4422256}, DOI={10.1109/isdrs.2007.4422256}, abstractNote={A theoretical study that explores the feasibility of a new spin-based nonvolatile memory concept is presented. The active region of the memory cell is a semiconductor quantum dot (QD) sharing an interface with a dielectric ferromagnetic layer (FML). The operating principle of the device is based on the spontaneous magnetic symmetry breaking due to exchange interaction between the magnetic ions in the FML and the spins of the itinerant holes in the QD. As a result, the formation of bistable states is possible at some conditions. We find the parameters window that admits the bistability and consider its lifetime (bit retention time) as the QD is scaled down. The analysis is carried out for two different QD materials: a non-magnetic (NM) QD and a diluted magnetic semiconductor (DMS) QD. In addition, two different designs are considered: a QD sharing an interface with the FML and a QD embedded in the FML. The proposed device is ready for scalability, potentially down to a few hole level by reducing the size of the QD, and it promises high integration density since only two terminals are used for device operation.}, booktitle={2007 International Semiconductor Device Research Symposium}, publisher={IEEE}, author={Enaya, Hani and Semenov, Yuriy G. and Kim, Ki Wook and Zavada, John M.}, year={2007}, month={Dec} }
 @article{semenov_kim_2007, title={Elastic spin-relaxation processes in semiconductor quantum dots}, volume={75}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.75.195342}, DOI={10.1103/physrevb.75.195342}, abstractNote={Electron spin decoherence caused by elastic spin-phonon processes is investigated comprehensively in a zero-dimensional environment. Specifically, a theoretical treatment is developed for the processes associated with the fluctuations in the phonon potential as well as in the electron procession frequency through the spin-orbit and hyperfine interactions in the semiconductor quantum dots. The analysis identifies the conditions (magnetic field, temperature, etc.) in which the elastic spin-phonon processes can dominate over the inelastic counterparts with the electron spin-flip transitions. Particularly, the calculation results illustrate the potential significance of an elastic decoherence mechanism originating from the intervalley transitions in semiconductor quantum dots with multiple equivalent energy minima (e.g., the X valleys in SiGe). The role of lattice anharmonicity and phonon decay in spin relaxation is also examined along with that of the local effective field fluctuations caused by the stochastic electronic transitions between the orbital states. Numerical estimations are provided for typical GaAs and Si-based quantum dots.}, number={19}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2007}, month={May} }
 @article{enaya_semenov_kim_zavada_2007, title={Electrical Manipulation of Nonvolatile Spin Cell Based on Diluted Magnetic Semiconductor Quantum Dots}, volume={54}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/TED.2007.894377}, DOI={10.1109/TED.2007.894377}, abstractNote={In this paper, electrical manipulation of a memory cell based on a semiconductor nanostructure consisting of a diluted magnetic semiconductor (DMS) quantum dot (QD) and a reservoir of itinerant holes separated by an energy barrier is investigated theoretically. The operating principle takes advantage of the paramagnetic-ferromagnetic (PM-FM) phase transition mediated by the itinerant holes in the DMS QD that can lead to electrically controlled write/erase operations. Nonvolatility can be achieved when the structure is properly designed to reach a thermodynamic equilibrium at both the PM and FM configurations (i.e., bistability). Assuming a parabolic confining potential in the QD, the performance characteristics of the proposed nanostructure are analyzed including the scalability and the lifetime. An advantage of this memory concept is the extremely small dissipative energy for write/erase functions due to the open-circuit nature of the process. A readout scheme enabling electrical detection, with the repetition rate up to the 10-100-MHz range, is also explored by utilizing only two contacts. Finally, a potential application of the proposed memory cell is discussed as a rudimentary device for logic AND and OR operations}, number={5}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Enaya, Hani and Semenov, Yuriy G. and Kim, K. W. and Zavada, John M.}, year={2007}, month={May}, pages={1032–1039} }
 @article{semenov_kim_iafrate_2007, title={Electron spin relaxation in semiconducting carbon nanotubes: The role of hyperfine interaction}, volume={75}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.75.045429}, DOI={10.1103/physrevb.75.045429}, abstractNote={A theory of electron spin relaxation in semiconducting carbon nanotubes is developed based on the hyperfine interaction with disordered nuclei spins $I=1∕2$ of $^{13}\mathrm{C}$ isotopes. It is shown that strong radial confinement of electrons enhances the electron-nuclear overlap and subsequently electron spin relaxation (via the hyperfine interaction) in the carbon nanotubes. The analysis also reveals an unusual temperature dependence of longitudinal (spin-flip) and transversal (dephasing) relaxation times: the relaxation becomes weaker with the increasing temperature as a consequence of the particularities in the electron density of states inherent in one-dimensional structures. Numerical estimations indicate relatively high efficiency of this relaxation mechanism compared to the similar processes in bulk diamond. However, the anticipated spin relaxation time of the order of $1\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ in carbon nanotubes is still much longer than those found in conventional semiconductor structures. Moreover, it is found that the curvature effect and subsequent rehybridization of $s$ and $p$ orbitals in ultrathin nanotubes may significantly impact the electron spin relaxation leading to its further suppression at certain dimensions.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W. and Iafrate, G. J.}, year={2007}, month={Jan} }
 @article{xiao_kim_zavada_2007, title={Imaging properties of a metallic photonic crystal}, volume={101}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2737771}, DOI={10.1063/1.2737771}, abstractNote={Imaging effects in metallic photonic crystals (PCs) are examined theoretically based on the finite difference time-domain method. The analysis shows that, in metallic PC-based systems, far-field images do form at the opposite side of the PC “lens” and more importantly, follow the rule of geometric optics with respect to the changes in the source position as a direct proof of negative refraction. However, the comparison of ideal left-handed media with a metallic PC suggests that the focusing effect in the PC based system is different from that of the ideal left-handed media in many aspects, due to the inhomogeneous nature of the PC. Particularly, strong dependence on the individual geometry as well as the frequency in the PC-based system renders the effective index sensitive to the variations and potentially limits its application as a superlens.}, number={11}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Xiao, D. and Kim, K. W. and Zavada, J. M.}, year={2007}, month={Jun}, pages={113105} }
 @article{sokolov_kim_kochelap_muntiian_2007, title={Negative small-signal impedance of nanoscale GaN diodes in the terahertz frequency regime}, volume={90}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2720758}, DOI={10.1063/1.2720758}, abstractNote={A physical mechanism of electrical instability in the terahertz frequency range is explored in a nanoscale two-terminal configuration of nitride-based structures under a high-field transport regime. The investigated instability utilizes the negative differential resistance effect that is known to occur in bulk group-III nitride semiconductors. A distinctive feature of the proposed mechanism for terahertz generation is that the diode steady-state I-V characteristics maintain a positive differential resistance for a stable operation, while the small-signal response provides negative impedance within the desired frequency range. An additional advantage is that the frequency window of negative small-signal impedance can be tuned electrically.}, number={14}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Sokolov, V. N. and Kim, K. W. and Kochelap, V. A. and Muntiian, P. M.}, year={2007}, month={Apr}, pages={142117} }
 @article{sokolov_kong_kim_trew_2007, title={Quasimonochromatic emission spectra in the near field by polar semiconductor thermal sources}, volume={90}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2713166}, DOI={10.1063/1.2713166}, abstractNote={The near-field spectra of the electromagnetic field emitted from a planar surface are theoretically investigated for a number of polar semiconductor and dielectric materials that support surface phonon polaritons. All of the studied materials, InP, GaAs, GaN, SiC, and α-Al2O3 (sapphire), exhibit quasimonochromatic thermal emission symbolized by strong peaks of evanescent modes at well-defined frequencies in the near field that correspond to the appropriate peaks in the density of states for surface phonon polaritons. It is also found that the materials with lower polariton frequencies (e.g., InP and GaAs) generally demonstrate a higher peak spectral energy density compared to those with higher frequencies (e.g., SiC). This trend is maintained over the entire range of temperature (300–600K) and the distance from the surface (⩽10μm) considered in the calculation. Thus, the results clearly indicate that among the studied materials InP and GaAs are the best candidates to provide the quasicoherent thermal emission for potential use as a nanoscale thermal source. The energy density stored in the evanescent peaks, when close to the surface, is estimated to be many orders of magnitude larger than that in the blackbody radiation.}, number={11}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Sokolov, V. N. and Kong, B. D. and Kim, K. W. and Trew, R. J.}, year={2007}, month={Mar}, pages={113106} }
 @article{semenov_kim_zavada_2007, title={Spin field effect transistor with a graphene channel}, volume={91}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.2798596}, DOI={10.1063/1.2798596}, abstractNote={A spin field effect transistor (FET) is proposed by utilizing a graphene layer as the channel. Similar to the conventional spin FETs, the device involves spin injection and spin detection by ferromagnetic source and drain. Due to the negligible spin-orbit coupling in the carbon based materials, spin manipulation in the channel is achieved via electrical control of the electron exchange interaction with a ferromagnetic gate dielectric. Numerical estimates indicate the feasibility of the concept if the bias can induce a change in the exchange interaction energy of the order of meV. When nanoribbons are used for a finite channel width, those with armchair-type edges can maintain the device stability against the thermal dispersion.}, number={15}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Semenov, Y. G. and Kim, K. W. and Zavada, J. M.}, year={2007}, month={Oct}, pages={153105} }
 @article{galatsis_wang_botros_yang_xie_stoddart_kaner_ozkan_liu_ozkan_et al._2006, title={Emerging memory devices}, volume={22}, ISSN={8755-3996}, url={http://dx.doi.org/10.1109/MCD.2006.1657845}, DOI={10.1109/mcd.2006.1657845}, abstractNote={Each memory device presented has its unique range of advantages and challenges. DRAM and FLASH have radically different characteristics; hence, they are used for different applications. Accordingly, the search for memory devices beyond CMOS comes with an important caveat: different memory for different applications. FENA's research path will continue to focus on improving our presented memory devices, and integrating with logic elements, while exploring other emerging memory devices based on nanomaterials, nanostructures, and the next generation of low-cost assembly techniques}, number={3}, journal={IEEE Circuits and Devices Magazine}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Galatsis, K. and Wang, Kang and Botros, Y. and Yang, Yang and Xie, Ya-Hong and Stoddart, J.F. and Kaner, R.B. and Ozkan, C. and Liu, Jianlin and Ozkan, M. and et al.}, year={2006}, month={May}, pages={12–21} }
 @article{kochelap_klimov_kim_2006, title={Optical phonon instability induced by high-speed electron transport in nanoscale semiconductor structures}, volume={73}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.73.035301}, DOI={10.1103/physrevb.73.035301}, abstractNote={We analyze the interaction of high-speed electrons and polar optical phonons in nanoscale semiconductor structures. Under the velocity overshoot regime, it is found that electrons can induce optical phonon instability (i.e., the lattice optical vibrations grow in time when the electric current exceeds a threshold value). For nanoscale diodes based on III-V compounds, the threshold current density is estimated to be of the order of $100\phantom{\rule{0.3em}{0ex}}\mathrm{kA}∕{\mathrm{cm}}^{2}$ and the corresponding bias $0.5--1.5\phantom{\rule{0.3em}{0ex}}\mathrm{V}$ for the diode lengths of $50--100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The wavelengths of unstable phonons are about $10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ with the characteristic time for instability development in the $10\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ range. We suggest that this phenomenon can lead to efficient generation of coherent optical phonons with a number of potential applications.}, number={3}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kochelap, V. A. and Klimov, A. A. and Kim, K. W.}, year={2006}, month={Jan} }
 @inproceedings{xiao_kim_zavada_lazzi_2006, title={Realization of tunable photonic crystals based on the metal insulator transition of VO 2}, url={http://dx.doi.org/10.1117/12.643920}, DOI={10.1117/12.643920}, abstractNote={The feasibility of an electrically programmable photonic crystal (PC) is investigated theoretically based on the metal-insulator transition of vanadium dioxide (VO2). We propose a slab structure based on VO2 whose dielectric properties can be modulated by selectively applying the bias on a lithographically defined array of gate electrodes to induce the phase transition. So, unlike the ordinary PCs, wave propagation in the desired structure may be switched on/off or redirected to our satisfaction. To examine the idea, the photonic band structure (PBS) and the wave guiding characteristics are investigated by using the iterative plane wave expansion and the finite difference time domain methods. The results clearly indicate that the changes induced in the VO2 dielectric properties via the phase transition can enable effective modulation of wave propagation at a high speed, offering a promising opportunity for a photonic circuit that can be programmed or reconfigured on demand.}, booktitle={Photonic Crystal Materials and Devices IV}, publisher={SPIE}, author={Xiao, D. and Kim, K. W. and Zavada, J. M. and Lazzi, G.}, editor={Adibi, Ali and Lin, Shawn-Yu and Scherer, AxelEditors}, year={2006}, month={Feb} }
 @article{tsen_kiang_ferry_kochelap_komirenko_kim_morkoc_2006, title={Subpicosecond Raman studies of electric-field-induced optical phonon instability in an In0.53Ga0.47As-based semiconductor nanostructure}, volume={18}, ISSN={0953-8984 1361-648X}, url={http://dx.doi.org/10.1088/0953-8984/18/34/009}, DOI={10.1088/0953-8984/18/34/009}, abstractNote={Transient carrier transport phenomena in an In0.53Ga0.47As-based p–i–n semiconductor nanostructure have been studied by using subpicosecond transient/time-resolved Raman spectroscopy. We observe an instability of the GaAs-like optical phonon population in this nanostructure semiconductor that occurs when electrons are accelerated to very high velocities by the application of intense electric fields. The results open up a new channel for creating coherent THz frequency that can be used in THz electronic devices. We suggest that the observed phenomena will have enormous impact on the carrier dynamics and carrier transport in nanoscale semiconductor electronic devices.}, number={34}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Tsen, K T and Kiang, Juliann G and Ferry, D K and Kochelap, V A and Komirenko, S M and Kim, K W and Morkoc, H}, year={2006}, month={Aug}, pages={7961–7974} }
 @article{xiao_kim_lazzi_zavada_2006, title={Tunable waveguiding in electrically programmable VO2-based photonic crystals}, volume={99}, ISSN={["1089-7550"]}, DOI={10.1063/1.2200873}, abstractNote={The feasibility of electrically programmable waveguiding in a photonic crystal (PC) is explored based on the metal-insulator transition of vanadium dioxide (VO2). Unlike the ordinary PCs, wave propagation in the desired structure may be switched on/off or redirected by applying an electrical bias on the selective electrodes by taking advantage of the electrically induced VO2 phase transition and subsequent modulation of dielectric properties. The characteristics of the two-dimensional VO2-based PCs with line defects are analyzed using the iterative plane wave and finite difference time domain methods. Particularly, the influence of the Drude relaxation on waveguiding is examined as the high rate typical for metallic VO2 can lead to the signal loss. An optimized structure is proposed to minimize the loss and simplify the fabrication.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Xiao, D. and Kim, K. W. and Lazzi, G. and Zavada, J. M.}, year={2006}, month={Jun} }
 @inproceedings{kiselev_kim_yablonovitch_2005, title={Analysis of the Δ(X) − L intervalley mixing in group-IV heterostructures}, volume={772}, ISSN={0094-243X}, url={http://dx.doi.org/10.1063/1.1994159}, DOI={10.1063/1.1994159}, abstractNote={We provide a treatment of the problem of Δ(X) − L intervalley mixing in differently oriented SiGe heterostructures in the transparent effective mass method. Mixing potentials can be calculated, considering changes in the constituent Concentrations of individual heterolayers from some “virtual crystal level” as a bunch of microscopic single‐ion perturbations. Strong mixing between lowest localized Δ and L states can be achieved in (113) structures, making them favorable for the electrically controlled gigantic intervalley g factor modulation. We provide estimates for the mixing potential and further consider limitations related to the strength of the in‐plane localization and quality of the interface.}, booktitle={AIP Conference Proceedings}, publisher={AIP}, author={Kiselev, A.A. and Kim, K.W. and Yablonovitch, E.}, year={2005}, pages={409–410,} }
 @article{semenov_enaya_kim_2005, title={Bistability in a magnetic and nonmagnetic double-quantum-well structure mediated by the magnetic phase transition}, volume={86}, ISSN={0003-6951}, url={http://dx.doi.org/10.1063/1.1864237}, DOI={10.1063/1.1864237}, abstractNote={The hole distribution in a double-quantum-well (QW) structure consisting of a magnetic and a nonmagnetic semiconductor QW is investigated as a function of temperature, the energy shift between the QWs, and other relevant parameters. When the itinerant holes mediate the ferromagnetic ordering, it is shown that a bistable state can be formed through hole redistribution, resulting in a significant change in the properties of the constituting magnetic QW (i.e., the paramagnetic-ferromagnetic transition). The model calculation also indicates a large window in the system parameter space where bistability is possible. Hence, this structure could form the basis of a stable memory element that may be scaled down to a few-hole regime.}, number={7}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Semenov, Y. G. and Enaya, H. and Kim, K. W.}, year={2005}, pages={073107} }
 @article{fedorov_sokolov_kim_zavada_2005, title={Coulombic effects of electron-hole plasma in nitride-based nanostructures}, volume={98}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2060937}, DOI={10.1063/1.2060937}, abstractNote={We study the Coulombic effects of electron-hole plasma on the ground and first excited energy levels and carrier wave functions in a GaN∕AlGaN quantum well (QW) structure. The coupled Schrödinger equations for electron and hole states are solved self-consistently in the Hartree-Fock approximation along with the Poisson equation. As expected, the decreasing QW width and increasing plasma density diminish the charge separation in the QW induced by the internal field, leading to the relatively reduced contribution of the Hartree interaction to the energy-level shift. In contrast, the calculation also demonstrates that the contribution of many-body effects becomes more pronounced. The resulting competition between the many-body and Hartree contributions causes a nonmonotonous dependence of the electron and hole energies on the plasma density at a given field. These findings are applied to explore the potential bistable behavior in the QW electroabsorption under near-band-edge photoexcitation.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Fedorov, I. A. and Sokolov, V. N. and Kim, K. W. and Zavada, J. M.}, year={2005}, month={Sep}, pages={063711} }
 @article{xiao_kim_zavada_2005, title={Electrically programmable photonic crystal slab based on the metal-insulator transition in VO2}, volume={97}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1898435}, DOI={10.1063/1.1898435}, abstractNote={The possibility of an electrically programmable photonic crystal is investigated theoretically based on the metal-insulator transition of vanadium dioxide (VO2). Recent experiments indicate that this phase transition of the first order can be controlled via external bias and results in significant changes in the electrical and optical properties of VO2. We propose a slab structure based on VO2 whose dielectric properties are modulated periodically in the in-plane direction by selectively inducing phase transition through a lithographically defined array of gate electrodes. A two-dimensional photonic band calculation predicts the presence of a band gap, clearly illustrating the feasibility of the proposed structure. The electrically controlled nature may enable the VO2- based structure to be programmable at a very high speed.}, number={10}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Xiao, D. and Kim, K. W. and Zavada, J. M.}, year={2005}, month={May}, pages={106102} }
 @article{glavin_kochelap_linnik_kim_2005, title={Electron-phonon interaction via the Pekar mechanism in nanostructures}, volume={71}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.71.081305}, DOI={10.1103/physrevb.71.081305}, abstractNote={We consider an electron-acoustic-phonon coupling mechanism associated with the dependence of crystal dielectric permittivity on the strain (the so-called Pekar mechanism) in nanostructures characterized by strong confining electric fields. The efficiency of Pekar coupling is a function of both the absolute value and the spatial distribution of the electric field. It is demonstrated that this mechanism exhibits a phonon wave-vector dependence similar to that of piezoelectricity and must be taken into account for electron transport calculations in nanostructures with extended field distributions. In particular, we analyze the role of Pekar coupling in energy relaxation in silicon inversion layers. Comparison with the recent experimental results is provided to illustrate its potential significance.}, number={8}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Glavin, B. A. and Kochelap, V. A. and Linnik, T. L. and Kim, K. W.}, year={2005}, month={Feb} }
 @inproceedings{fedorov_kim_sokolov_zavada_2005, title={Exchange Effects on Electronic States in QWs with e-h Plasma in an Electric Field}, volume={772}, ISSN={0094-243X}, url={http://dx.doi.org/10.1063/1.1994559}, DOI={10.1063/1.1994559}, abstractNote={We study effects of electron‐hole (e‐h) plasma density N and a uniform electric field F on the ground and first excited eigenstates, energy levels and electron and hole wave functions, resulting from many‐particle (Hartree and exchange) Coulomb interactions in a 2D e‐h plasma. The coupled Schrodinger equations for electrons and holes are solved self‐consistently in the Hartree‐Fock approximation together with the Poisson equation. The solutions are analyzed treating N and F as independent parameters for quantum wells (QWs) with different width, dqw. The calculations demonstrate that with decreasing dqw and increasing N, the charge separation within the QW induced by the field becomes less effective and the relative contribution of the Hartree interactions to the energy level shifts is decreased. The results are applied to study possible bistable behavior of the QW electroabsorption under strong photoexcitation near the exciton resonance.}, booktitle={AIP Conference Proceedings}, publisher={AIP}, author={Fedorov, I.A. and Kim, K.W. and Sokolov, V.N. and Zavada, J.M.}, year={2005}, pages={1234–1235,} }
 @article{kim_sokolov_kochelap_korotyeyev_woolard_2005, title={High-speed and high-frequency electron effects in nitride semiconductors for terahertz applications}, volume={2}, ISSN={1610-1634 1610-1642}, url={http://dx.doi.org/10.1002/pssc.200461372}, DOI={10.1002/pssc.200461372}, abstractNote={We discuss the basic properties of the transient hot-electron transport and dynamic mobility in group-III nitrides under dominant electron–polar-optical-phonon scattering determining their capability for applications in THz frequency range. For bulk samples with high electron concentration, we provide the phase-plane analysis of the time-dependent transient transport and classification of different transient regimes depending on the initial conditions. The calculations predict a frequency interval with negative dynamic electron mobility where the amplification and generation of microwaves in THz frequency range is possible. For quantum-well heterostructures with low electron concentration under the streaming regime at moderate fields, we have revealed THz frequency windows of the negative microwave mobility, which enables the development of a tunable THz laser based on nitride quantum heterostructures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={7}, journal={physica status solidi (c)}, publisher={Wiley}, author={Kim, K. W. and Sokolov, V. N. and Kochelap, V. A. and Korotyeyev, V. V. and Woolard, D. L.}, year={2005}, month={May}, pages={2569–2572} }
 @inproceedings{kiselev_baron_kim_wang_yablonovitch_2005, title={L-valley electrons in SiGe heterostructures: highly anisotropic and tunable Zeeman and Rashba-like spin splittings}, volume={772}, ISSN={0094-243X}, url={http://dx.doi.org/10.1063/1.1994160}, DOI={10.1063/1.1994160}, abstractNote={We have conducted a detailed and systematic analysis of Zeeman and Rashba‐like (structure‐asymmetry‐induced) spin splittings in SiGe heterostructures. The calculations were performed in the framework of a relevant kp model, developed specifically for the L point states of the group IV semiconductors. Effects of the alloy composition, crystallographic orientation, spatial confinement, strain, and electric field are accounted for and documented for a realistic structure design. Notable Rashba effect, considerable anisotropy and deviation of the g tensor components from their respective bulk values make the SiGe structures a friendly choice for the effective spin manipulation.}, booktitle={AIP Conference Proceedings}, publisher={AIP}, author={Kiselev, A.A. and Baron, F.A. and Kim, K.W. and Wang, K.L. and Yablonovitch, E.}, year={2005}, pages={411–412,} }
 @inproceedings{kim_sokolov_kochelap_korotyeyev_woolard_2005, title={Nitride-based two-terminal oscillators operating in the THz regime}, url={http://dx.doi.org/10.1117/12.602975}, DOI={10.1117/12.602975}, abstractNote={We present a theoretical study of two-terminal nitride-based oscillators utilizing two different hot-electron transport regimes determined by the interaction of the electrons with polar optical phonons, which are capable to generate current/voltage oscillations in the THz-frequency range. The first is the limited space-charge accumulation (LSA) regime based on the negative differential resistance (NDR) in a bulk-like GaN structure at room temperature at high electric field E > Et (Et ≈ 150 kV/cm). The second is the streaming regime in a quantum well (QW) structure in moderate electric field (1-10 kV/cm) at the nitrogen temperature or higher. The latter corresponds to the optical-phonon transit-time (OPTT) resonance and typically does not lead to an NDR at zero frequency. We show that for both regimes, real part of the electron dynamic mobility can be negative within certain THz-frequency windows, whose location and width depend on E. For a 100-nm n-GaN diode with a cross-section of 500 μm2 and the electron density of 1×1017 cm-3, the generated microwave power is estimated to be ≈ 0.6 W with the dc-to-rf conversion efficiency ≈ 9 % and the magnitude of the NDR of -1.3 Ω. When the streaming transport is realized in the QW channel, the generated power is estimated to be about 350 mW with the efficiency of few percent for a ten QWs GaN-based structure. Hence, the investigated transport mechanisms provide efficient mean to achieve very high-frequency microwave generation in the nitrides.}, booktitle={Terahertz for Military and Security Applications III}, publisher={SPIE}, author={Kim, K. W. and Sokolov, V. N. and Kochelap, V. A. and Korotyeyev, V. V. and Woolard, D. L.}, editor={Hwu, R. Jennifer and Woolard, Dwight L. and Rosker, Mark J.Editors}, year={2005}, month={May} }
 @article{semenov_kim_2005, title={Nonvolatile bistability effect based on the electrically controlled phase transition in scaled magnetic semiconductor nanostructures}, volume={72}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.72.195303}, DOI={10.1103/physrevb.72.195303}, abstractNote={We explore the bistability effect in a dimensionally scaled semiconductor nanostruncture consisting of a diluted magnetic semiconductor quantum dot (QD) and a reservoir of itinerant holes separated by a barrier. The bistability stems from the magnetic phase transition in the QD mediated by the changes in the hole population. Our calculation shows that when properly designed, the thermodynamic equilibrium of the scaled structure can be achieved at two different configurations; i.e., the one with the QD in a ferromagnetic state with a sufficient number of holes and the other with the depopulated QD in a paramagnetic state. Subsequently, the parameter window suitable for this bistability formation is discussed along with the the conditions for the maximum robustness/non-volatility. To examine the issue of scaling, an estimation of the bistabiity lifetime is made by considering the thermal fluctuation in the QD hole population via the spontaneous transitions. A numerical evaluation is carried out for a typical carrier-mediated magnetic semiconductor (e.g., GaMnAs) as well as for a hypothetical case of high Curie temperature for potential room temperature operation.}, number={19}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2005}, month={Nov} }
 @article{kiselev_kim_2005, title={Prohibition of equilibrium spin currents in multiterminal ballistic devices}, volume={71}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.71.153315}, DOI={10.1103/physrevb.71.153315}, abstractNote={We show that in the multi-terminal ballistic devices with intrinsic spin-orbit interaction connected to normal metal contacts there are no equilibrium spin currents present at any given electron energy. Obviously, this statement holds also after the integration over all occupied states. Based on the proof of this fact, a number of scenarios involving nonequilibrium spin currents is identified and further analyzed. In particular, it is shown that an arbitrary two-terminal device cannot polarize transient current. The same is true for the output terminal of an N-terminal device when all N-1 inputs are connected in parallel.}, number={15}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kiselev, A. A. and Kim, K. W.}, year={2005}, month={Apr} }
 @article{glavin_kim_2005, title={Spin relaxation of two-dimensional holes in strained asymmetric SiGe quantum wells}, volume={71}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.71.035321}, DOI={10.1103/physrevb.71.035321}, abstractNote={We analyze spin splitting of the two-dimensional hole spectrum in strained asymmetric SiGe quantum wells (QWs). Based on the Luttinger Hamiltonian, we obtain expressions for the spin-splitting parameters up to the third order in the in-plane hole wave vector. The biaxial strain of SiGe QWs is found to be a key parameter that controls spin splitting. Application to SiGe field-effect transistor structures indicates that typical spin splitting at room temperature varies from a few tenths of meV in the case of Si QW channels to several meV for the Ge counterparts, and can be modified efficiently by gate-controlled variation of the perpendicular confining electric field. The analysis also shows that for sufficiently asymmetric QWs, spin relaxation is due mainly to the spin-splitting related D'yakonov-Pere\ifmmode \acute{l}\else \'{l}\fi{} mechanism. In strained Si QWs, our estimation shows that the hole spin relaxation time can be on the order of 100 picoseconds at room temperature, suggesting that such structures are suitable for $p$-type spin transistor applications as well.}, number={3}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Glavin, B. A. and Kim, K. W.}, year={2005}, month={Jan} }
 @article{sokolov_kim_kochelap_woolard_2005, title={Terahertz generation in submicron GaN diodes within the limited space-charge accumulation regime}, volume={98}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.2060956}, DOI={10.1063/1.2060956}, abstractNote={The conditions for microwave power generation with hot-electron transport are investigated in a submicron GaN diode when it operates in the limited space-charge accumulation (LSA) mode. Applying a transport model based on the local quasistatic approximation, the analysis shows that the nitride diodes can support the LSA mode of oscillation in the terahertz-frequency range. For a 100nm n-GaN diode with a cross section of 500μm2 and the electron density of 1×1017cm−3, the generated microwave power is estimated to be as high as ≈0.6W with the corresponding dc-to-rf conversion efficiency of ≈9% and the negative differential resistance of ≈−1.3Ω; which thus provides an efficient mechanism to achieve very high-frequency microwave generation in the nitrides.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Sokolov, V. N. and Kim, K. W. and Kochelap, V. A. and Woolard, D. L.}, year={2005}, month={Sep}, pages={064507} }
 @inproceedings{xiao_kim_bedair_zavada_2004, title={Analysis of nitride-based quantum well LEDs and novel white LED design}, url={http://dx.doi.org/10.1117/12.524424}, DOI={10.1117/12.524424}, abstractNote={Fundamental electrical and optical properties of strained wurtzite InGaN/GaN-based quantum well light emitting diodes are calculated based on the Rashba-Sheka-Pikus Hamiltonian in the vicinity of the Gamma point. The theoretical results show an excellent correlation with experiments. A novel design of using AlInGaN as quantum barrier is proposed to realize efficient red emission, which is hard to achieve if GaN is used as barrier. To achieve high efficiency, the important factors relating to the oscillator strength are discussed in detail.}, booktitle={Light-Emitting Diodes: Research, Manufacturing, and Applications VIII}, publisher={SPIE}, author={Xiao, Dong and Kim, Ki W. and Bedair, Salah M. and Zavada, John M.}, editor={Stockman, Steve A. and Yao, H. Walter and Schubert, E. FredEditors}, year={2004}, month={Jun} }
 @article{semenov_kim_2004, title={Correlation of phonon decay with localized electron spin-phase diffusion}, volume={70}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.70.085305}, DOI={10.1103/physrevb.70.085305}, abstractNote={A spin decoherence mechanism is proposed for localized electrons. The irregular phonon phase disturbances originated from phonon relaxation can influence electron spin precession with a net effect of spin phase decay. A quantitative analysis demonstrates relatively high efficiency of this mechanism in the low temperature and low magnetic field regime compared to the spin-flip processes.}, number={8}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2004}, month={Aug} }
 @article{xiao_kim_bedair_zavada_2004, title={Design of white light-emitting diodes using InGaN/AlInGaN quantum-well structures}, volume={84}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1644920}, DOI={10.1063/1.1644920}, abstractNote={Based on the Rashba–Sheka–Pikus Hamiltonian in the vicinity of the Γ point, and taking into consideration spontaneous and piezoelectric polarization, the optical intensity of nitride-based quantum-well light-emitting diodes has been calculated. It is found that strain substantially alters the subband structure and thus the output intensity of these nitride-biased quantum-well light-emitting diodes. A design that uses AlInGaN as the quantum barrier is proposed to realize efficient red emission, which is hard to achieve if GaN is used as the barrier. In the proposed design, three different InGaN/AlInGaN quantum-well structures emit red, green, and blue light of similar intensity. Also, to achieve high efficiency, important factors related to the oscillator strength are discussed in detail.}, number={5}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Xiao, D. and Kim, K. W. and Bedair, S. M. and Zavada, J. M.}, year={2004}, month={Feb}, pages={672–674} }
 @article{xiao_kim_zavada_2004, title={Envelope-function analysis of wurtzite InGaN/GaN quantum well light emitting diodes}, volume={96}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1755435}, DOI={10.1063/1.1755435}, abstractNote={Fundamental electrical and optical properties of strained wurtzite InGaN/GaN-based quantum-well light-emitting diodes are calculated based on the Rashba–Sheka–Pikus Hamiltonian in the vicinity of the Γ point. It is found that the strain and the strain-induced piezoelectric field significantly alter the subband structure and determines the output intensity of the nitride quantum well light emitting diodes. For the case with high In composition (≳0.2), the calculation also supports the possibility of strain relaxation in the quantum well. Coupled with an optimized set of parameters, our theoretical model provides an excellent agreement with the available experimental data over a wide range of In composition (0–0.5).}, number={1}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Xiao, D. and Kim, K. W. and Zavada, J. M.}, year={2004}, month={Jul}, pages={723–728} }
 @article{sokolov_kim_kochelap_woolard_2004, title={High-frequency small-signal conductivity of hot electrons in nitride semiconductors}, volume={84}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1738518}, DOI={10.1063/1.1738518}, abstractNote={We investigate the small-signal conductivity of the electrons in group-III nitrides under a high steady-state electric field. The resulting calculation indicates a frequency dependence of the conductivity that is drastically different from that given by the Drude formula. A large and very fast response of the hot electrons in the nitrides is revealed. The complex conductivity is found to be finite up to the frequency of about 10 THz. For the fields above the threshold corresponding to the peak drift velocity, the calculation also predicts a frequency interval with a negative conductivity. A detailed analysis is provided on the field and frequency dependence of the dynamic conductivity at the high electric fields.}, number={18}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Sokolov, V. N. and Kim, K. W. and Kochelap, V. A. and Woolard, D. L.}, year={2004}, month={May}, pages={3630–3632} }
 @article{komirenko_kim_kochelap_woolard_2004, title={Low-field electron runaway and spontaneous formation of two-beam velocity distribution in polar semiconductors}, volume={69}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.69.233201}, DOI={10.1103/physrevb.69.233201}, abstractNote={We show that high-energy electron injection into a polar semiconductor can lead to a spontaneous splitting of the electron beam into two distinct groups with different velocity distributions. While one group of electrons experiences thermalization in a given subthreshold field, the velocity and energy of the second group increases with distance due to the previously unknown low-field electron runaway effect. We investigate the dependence of the carrier distribution on the injection energy, and show that the overall distribution exhibits a partial population inversion with a distance-dependent energy gap between the thermalized and runaway electrons. The low-field runaway is a universal effect which is characteristic of nanoscale semiconductors where polar optical phonon scattering predominates and there is a large intervalley energy separation as in the group-III nitride heterostructures.}, number={23}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Komirenko, S. M. and Kim, K. W. and Kochelap, V. A. and Woolard, D. L.}, year={2004}, month={Jun} }
 @article{glavin_kochelap_linnik_kim_2004, title={Pekar mechanism of electron-phonon interaction in nanostructures}, volume={1}, ISSN={1610-1634 1610-1642}, url={http://dx.doi.org/10.1002/pssc.200405339}, DOI={10.1002/pssc.200405339}, abstractNote={We propose a new mechanism of electron-acoustic phonon interaction in nanostructures. It is related to appearance of macroscopic electric potential in external electric field under the phonon-strain-induced modulation of dielectric permittivity. For the case of bulk semiconductors this mechanism was introduced by Pekar for materials with very large dielectric permittivity. We show, that for nanostructures it becomes important for ordinary materials as well due to the presence of very strong confining electric fields. It is demonstrated, that in nanostructures not only the absolute value of the electric field, but also its spatial distribution is important. We consider the specific example of Pekar interaction contribution to the electron energy relaxation process in silicon inversion layers, where it leads to the piezoelectric-like dependence of the dissipated power. Finally, we discuss relevance of Pekar interaction to results of recent measurements of electron transport characteristics in silicon nanostructures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={11}, journal={physica status solidi (c)}, publisher={Wiley}, author={Glavin, B.A. and Kochelap, V.A. and Linnik, T.L. and Kim, K.W.}, year={2004}, month={Nov}, pages={2779–2782} }
 @article{sokolov_kim_kochelap_woolard_2004, title={Phase-plane analysis and classification of transient regimes for high-field electron transport in nitride semiconductors}, volume={96}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1808900}, DOI={10.1063/1.1808900}, abstractNote={We present a detailed theoretical analysis of steady-state, transient time-dependent, and spatially dependent electron transport in the group-III nitrides at high and ultrahigh electric fields. To develop an analytical model, we derive time-dependent differential equations describing the hot-electron rates of momentum and energy relaxation in electron–polar-optical-phonon scattering and analyze them by employing phase-plane analysis. From the structure of the phase-plane partitioning based on the phase trajectories, the transient regimes are investigated and classified depending on various initial conditions. We have studied different subpicosecond regimes and found a considerable velocity overshoot effect. One of our findings is that when the velocity reaches the maximum, the electron temperature is of a moderate magnitude but increases considerably in the subsequent stage. Dynamic regimes with high electron temperature overshoot have been revealed. For the dominant electron–polar-optical-phonon scattering, the observed overshoot can be treated as a rudiment of the runaway effect typical for that mechanism. In nanoscale nitride diodes with space-charge limited transport, the transient processes are extended to sufficiently larger distances, the overshoot is weaker and the electron heating in the region of the peak velocity is greater than that found for time-dependent problem with a constant electric field throughout a homogeneous sample.}, number={11}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Sokolov, V. N. and Kim, K. W. and Kochelap, V. A. and Woolard, D. L.}, year={2004}, month={Dec}, pages={6492–6503} }
 @article{semenov_kim_2004, title={Phonon-Mediated Electron-Spin Phase Diffusion in a Quantum Dot}, volume={92}, ISSN={0031-9007 1079-7114}, url={http://dx.doi.org/10.1103/PhysRevLett.92.026601}, DOI={10.1103/physrevlett.92.026601}, abstractNote={An effective spin relaxation mechanism that leads to electron spin decoherence in a quantum dot is proposed. In contrast with the common calculations of spin-flip transitions between the Kramers doublets, we take into account a process of phonon-mediated fluctuation in the electron spin preces-sion and subsequent spin phase diffusion. Specifically, we consider modulations in the longitudinal g factor and hyperfine interaction induced by the phonon-assisted transitions between the lowest electronic states. Prominent differences in the temperature and magnetic field dependence between the proposed mechanism and the spin-flip transitions are expected to facilitate its experimental verification. Numerical estimation demonstrates highly efficient spin relaxation in typical semiconductor quantum dots.}, number={2}, journal={Physical Review Letters}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2004}, month={Jan} }
 @article{glavin_kim_2004, title={Resonance-like electrical control of electron spin for microwave measurement}, volume={85}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1773359}, DOI={10.1063/1.1773359}, abstractNote={We demonstrate that the spin-polarized electron current can interact with a microwave electric field in a resonant manner. The spin–orbit interaction gives rise to an effective magnetic field proportional to the electric current. In the presence of both dc and ac electric field components, electron spin resonance occurs if the ac frequency matches the spin precession frequency that is controlled by the dc field. In a device consisting of two spin-polarized contacts connected by a two-dimensional channel, this mechanism allows electrically tuned detection of the ac signal frequency and amplitude. For GaAs, such detection is effective in the frequency domain around tens of gigahertz.}, number={3}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Glavin, B. A. and Kim, K. W.}, year={2004}, month={Jul}, pages={428–430} }
 @article{semenov_kim_2004, title={Spin polaron and bistability in ferromagnetic semiconductor quantum structures}, volume={70}, ISSN={1098-0121 1550-235X}, url={http://dx.doi.org/10.1103/PhysRevB.70.125303}, DOI={10.1103/physrevb.70.125303}, abstractNote={This work shows that the in-plane localization of a hole confined in a ferromagnetic semiconductor quantum well (QW) can lead to significant energy gain if spontaneous easy-plane magnetization is mediated by the mechanisms other than itinerant carriers. The hole spin normal to the QW plane reorients the in-plane magnetization of the ferromagnetic layer at the location of polaron formation, resulting in an exchange potential with a discrete level of localization. A flexible model that incorporates the magnetization gradient term, as well as magnetic anisotropy, is proposed. In contrast to the calculations of magnetic polaron in the paramagnetic semiconductors, the energy of spin polaron in a ferromagnetic semiconductor is almost independent of the temperature in a wide range below the critical temperature of phase transition. Our calculation also demonstrates the existence of bistability in the hole state when the structure consists of appropriate ferromagnetic and nonmagnetic QWs separated by a finite barrier. Hence, a memory element that can be scaled down to a single hole may be achieved through polaron formation.}, number={12}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2004}, month={Sep} }
 @article{kim_korotyeyev_kochelap_klimov_woolard_2004, title={Tunable terahertz-frequency resonances and negative dynamic conductivity of two-dimensional electrons in group-III nitrides}, volume={96}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1811388}, DOI={10.1063/1.1811388}, abstractNote={We investigated the terahertz (THz)-frequency resonances of two-dimensional electron conductivity under the streaming transport in a GaN quantum well at the nitrogen temperature. The calculation results found that the negative microwave mobility can occur in the narrow windows near the optical-phonon transit-time resonance frequencies, which can be tuned electrically in the 0.2–2.5THz range with the static electric fields of 1–10kV∕cm. The estimated magnitude of the negative mobility reaches hundreds of cm2∕Vs. These effects suggest that the nitride-based heterostructure may enable the development of an electrically pumped, tunable THz source operating at or above 77K.}, number={11}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kim, K. W. and Korotyeyev, V. V. and Kochelap, V. A. and Klimov, A. A. and Woolard, D. L.}, year={2004}, month={Dec}, pages={6488–6491} }
 @inproceedings{komirenko_kim_kochelap_stroscio_2003, title={Coherent LO phonons generated by high-velocity electrons in two-dimensional channels and their impact on carrier transport}, ISBN={0780375386}, url={http://dx.doi.org/10.1109/NANO.2002.1032107}, DOI={10.1109/NANO.2002.1032107}, abstractNote={We show that Cerenkov generation of confined LO phonons by drifting electrons can be achieved in biased quantum wells (QWs). Both linear and nonlinear regimes of phonon generation are analyzed. The kinetic parameters of the drifting electrons are estimated by using momentum and energy balance equations for electron scattering by the confined optical phonons. Our findings suggest that high efficiency electrical generation of coherent optical phonons can be realized in two-dimensional structures with high drift velocities, such as AlAs/GaAs/AlAs and GaSb/InSb/GaSb QWs. Due to high conversion efficiency, the effect of current driven phonon generation can be an important mechanism of current suppression in two-dimensional channels where its contribution to saturation of current-voltage characteristics can compete with the contribution of intervalley transitions.}, booktitle={Proceedings of the 2nd IEEE Conference on Nanotechnology}, publisher={IEEE}, author={Komirenko, S.M. and Kim, K.W. and Kochelap, V.A. and Stroscio, M.A.}, year={2003}, month={Jun} }
 @article{semenov_kim_2003, title={Effect of an external magnetic field on electron-spin dephasing induced by hyperfine interaction in quantum dots}, volume={67}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.67.073301}, DOI={10.1103/physrevb.67.073301}, abstractNote={We investigate the influence of an external magnetic field on spin-phase relaxation of single electrons in semiconductor quantum dots induced by the hyperfine interaction. The basic decay mechanism is attributed to the dispersion of local effective nuclear fields over the ensemble of quantum dots. The characteristics of electron-spin dephasing are analyzed by taking an average over the nuclear-spin distribution. We find that the dephasing rate can be estimated as a spin-precession frequency caused primarily by the mean value of the local nuclear magnetic field. Furthermore, it is shown that the hyperfine interaction does not fully depolarize electron spin. The loss of initial spin polarization during the dephasing process depends strongly on the external magnetic field, leading to the possibility of effective suppression of this mechanism.}, number={7}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Kim, K. W.}, year={2003}, month={Feb} }
 @article{zavada_komirenko_kim_kochelap_2003, title={Efficient nitride-based short-wavelength emitters with enhanced hole injection}, volume={174}, number={2003}, journal={Compound Semiconductors 2002}, author={Zavada, J. M. and Komirenko, S. M. and Kim, K. W. and Kochelap, V. A.}, year={2003}, pages={401–404} }
 @article{barry_kiselev_kim_2003, title={Electron spin relaxation under drift in GaAs}, volume={82}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1578180}, DOI={10.1063/1.1578180}, abstractNote={Based on a Monte Carlo method, we investigate the influence of transport conditions on the electron spin relaxation in GaAs. The decay of initial electron spin polarization is calculated as a function of distance under the presence of moderate drift fields and/or nonzero injection energies. For relatively low fields (a couple of kV/cm), a substantial amount of spin polarization is preserved for several microns at 300 K. However, it is also found that the spin relaxation rate increases rapidly with the drift field, scaling as the square of the electron wave vector in the direction of the field. When the electrons are injected with a high energy, a pronounced decrease is observed in the spin relaxation length due to an initial increase in the spin precession frequency. Hence, high-field or high-energy transport conditions may not be desirable for spin-based devices.}, number={21}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Barry, E. A. and Kiselev, A. A. and Kim, K. W.}, year={2003}, month={May}, pages={3686–3688} }
 @article{komirenko_kim_kochelap_zavada_2003, title={Enhancement of hole injection for nitride-based light-emitting devices}, volume={47}, ISSN={0038-1101}, url={http://dx.doi.org/10.1016/S0038-1101(02)00314-3}, DOI={10.1016/S0038-1101(02)00314-3}, abstractNote={A novel device design is proposed for a strong enhancement of hole injection current in nitride-based light-emitting heterostructures. Preliminary calculations show orders of magnitude increase in injected hole current when using the proposed superlattice hole injector device based on the real-space transfer concept.}, number={1}, journal={Solid-State Electronics}, publisher={Elsevier BV}, author={Komirenko, S.M and Kim, K.W and Kochelap, V.A and Zavada, J.M}, year={2003}, month={Jan}, pages={169–171} }
 @article{baron_kiselev_robinson_kim_wang_yablonovitch_2003, title={Manipulating theL-valley electrongfactor in Si-Ge heterostructures}, volume={68}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.68.195306}, DOI={10.1103/physrevb.68.195306}, abstractNote={The Zeeman effect for the L valley conduction band electrons in SiGe heterostructures is considered. A detailed calculation of the electron g tensor is performed in the framework of a relevant kip model, developed specifically for the L point of the Brillouin zone. Electrons at the L point are considered under the influence of the different crystallographic orientations, alloy composition, quantum confinement, strain, and electric field, whose interplay causes a considerable deviation of the g tensor components from their bulk values. Our result strongly suggests that the SiGe-based quantum wells are a promising choice for the g tensor engineering for spin manipulation.}, number={19}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Baron, F. A. and Kiselev, A. A. and Robinson, H. D. and Kim, K. W. and Wang, K. L. and Yablonovitch, E.}, year={2003}, month={Nov} }
 @article{komirenko_kim_kochelap_koroteev_stroscio_2003, title={Nonlinear regimes of coherent optical phonon generation in quantum wells under electric current pumping}, volume={68}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.68.155308}, DOI={10.1103/physrevb.68.155308}, abstractNote={We present an analysis of nonlinear regimes of the coherent optical phonon generation under the electron drift in quantum wells. The phonon and electron subsystems are treated self-consistently. This allows us to find thesteady-state generation regimes with macroscopic populations of optical phonon modes and the electron transport controlled in part by the generated phonons. The generation regimes demonstrate a pronounced threshold character. At high electric fields above the threshold, practically single-mode generation occurs and the current-voltage characteristic is considerably changed. We demonstrate high efficiency generation of the coherent optical phonons by the electric current. The coherent macroscopic optical displacements and the amplitudes of oscillating electrostatic fields are evaluated. The proposed model based on the electron nonlinearities predicts a range of the pumping electric fields under which the steady state phonon generation is realized. Our results suggest that the phonon avalanche occurs beyond this field range.}, number={15}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Komirenko, S. M. and Kim, K. W. and Kochelap, V. A. and Koroteev, V. V. and Stroscio, M. A.}, year={2003}, month={Oct} }
 @inproceedings{liang_tsen_sankey_komirenko_kim_kochelap_wu_ho_ho_morkoc_2003, title={Observation of field-induced optical phonon amplification in semiconductor nanostructures}, url={http://dx.doi.org/10.1117/12.479278}, DOI={10.1117/12.479278}, abstractNote={We have experimentally proven the Cerenkov generation of optical phonons by drifting electrons in a semiconductor. We observe an instability of the polar optical phonons in nanoscale semiconductors that occurs when electrons are accelerated to very high velocities by intense electric fields. The instability is observed when the electron drift velocity is larger than the phase velocity of optical phonons and rather resembles a “sonic-boom” for optical phonons. The effect is demonstrated in p-i-n semiconductor nanostructures by suing subpicosecond Raman spectroscopy. We suggest that the observed phenomena will have enormous impact on the carrier dynamics in nanoscale semiconductor devices.}, booktitle={Ultrafast Phenomena in Semiconductors VII}, publisher={SPIE}, author={Liang, W. and Tsen, Kong-Thon F. and Sankey, Otto F. and Komirenko, Sergiy M. and Kim, Ki Wook and Kochelap, Viatcheslav A. and Wu, Meng-Chyi and Ho, Chong-Long and Ho, Wen-Jeng and Morkoc, Hadis}, editor={Tsen, Kong-Thon F. and Song, Jin-Joo and Jiang, HongxingEditors}, year={2003}, month={Jun} }
 @article{liang_tsen_sankey_komirenko_kim_kochelap_wu_ho_ho_morkoç_2003, title={Observation of optical phonon instability induced by drifting electrons in semiconductor nanostructures}, volume={82}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1563730}, DOI={10.1063/1.1563730}, abstractNote={We have experimentally proven the Cerenkov generation of optical phonons by drifting electrons in a semiconductor. We observe an instability of the polar optical phonons in nanoscale semiconductors that occurs when electrons are accelerated to very high velocities by intense electric fields. The instability is observed when the electron drift velocity is larger than the phase velocity of optical phonons and rather resembles a “sonic boom” for optical phonons. The effect is demonstrated in p–i–n semiconductor nanostructures by using subpicosecond Raman spectroscopy.}, number={12}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Liang, W. and Tsen, K. T. and Sankey, Otto F. and Komirenko, S. M. and Kim, K. W. and Kochelap, V. A. and Wu, Meng-Chyi and Ho, Chong-Long and Ho, Wen-Jeng and Morkoç, H.}, year={2003}, month={Mar}, pages={1968–1970} }
 @article{glavin_kim_2003, title={Spin-lattice relaxation in Si quantum dots}, volume={68}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.68.045308}, DOI={10.1103/physrevb.68.045308}, abstractNote={We consider spin-lattice relaxation processes for electrons trapped in lateral Si quantum dots in a [001] inversion layer. Such dots are characterized by strong confinement in the direction perpendicular to the surface and much weaker confinement in the lateral direction. The spin relaxation is assumed to be due to the modulation of electron g-factor by the phonon-induced strain, as was shown previously for the shallow donors. The results clearly indicate that the specific valley structure of the ground electron state in Si quantum dots causes strong anisotropy for both the one-phonon and two-phonon spin-relaxation rates. In addition, it gives rise to a partial suppression of the two-phonon relaxation in comparison to the spin relaxation of donor electrons.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Glavin, B. A. and Kim, K. W.}, year={2003}, month={Jul} }
 @article{korotyeyev_kochelap_kim_woolard_2003, title={Streaming distribution of two-dimensional electrons in III-N heterostructures for electrically pumped terahertz generation}, volume={82}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1569039}, DOI={10.1063/1.1569039}, abstractNote={We studied anisotropic electron distributions in group-III-nitride quantum wells and analyzed formation of the streaming regime under moderate electric fields. We found that the streaming effect can occur in high-mobility heterostructures (μ⩾30 000 cm2/V s) with low electron concentrations (n⩽1012 cm−2) at temperatures above 77 K. The effect holds in the electric fields of a few kV/cm. These conditions can be met in contemporary high-quality nitride heterostructures that have advantages over the bulk materials due to the specifics of electron–phonon and electron–electron interactions in two-dimensional structures. Subsequently, the streaming effect may enable the development of electrically-pumped THz sources operating above the nitrogen temperature based on nitride heterostructures.}, number={16}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Korotyeyev, V. V. and Kochelap, V. A. and Kim, K. W. and Woolard, D. L.}, year={2003}, month={Apr}, pages={2643–2645} }
 @article{kiselev_kim_2003, title={T-shaped spin filter with a ring resonator}, volume={94}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1601313}, DOI={10.1063/1.1601313}, abstractNote={A planar ballistic T-shaped structure with a ring resonator attached is shown to be highly effective in filtering electron spin from an unpolarized source into two output fluxes with opposite and practically pure spin polarizations. The operability of the proposed device relies on the peculiar spin-dependent transmission properties of the T-shaped connector in the presence of Rashba spin–orbit interaction as well as the difference in dynamic phase gain of the two alternative paths around the ring resonator through upper and lower branches for even and odd eigenmodes.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kiselev, A. A. and Kim, K. W.}, year={2003}, month={Sep}, pages={4001–4005} }
 @inproceedings{kim_komirenko_kochelap_stroscio_2002, title={Cerenkov generation of confined acoustic and optical phonons in quantum wells}, url={http://dx.doi.org/10.1117/12.470408}, DOI={10.1117/12.470408}, abstractNote={It is well known for bulk semiconductors that amplification (generation) of a phonon mode can be achieved via the Cerenkov effect when the electron drift velocity exceeds the phonon phase velocity. The following three requirements are necessary for practical use of this effect: high electron mobilities, large electron densities, and strong coupling between electrons and phonons. In this report we show that in quantum well heterostructures these requirements can be met and both confined acoustic and confined optical phonon modes can be efficiently generated (amplified) by the drift of two-dimensional carriers. General formulae for the gain coefficient as a function of the acoustic phonon frequency and structure parameters as well as for the confined phonon increment are derived. Taking into account the electron-acoustic-phonon interaction through the deformation potential as well as the piezoelectric interaction, we found that amplification coefficient can reach hundreds of 1/cm for the AlGaAs-based heterostructures and thousands of 1/cm for the SiGe-based heterostructures in the terahertz phonon frequency range. Amplification takes place in a spectrally separated and relatively narrow amplification bands. We show that the optical phonon increment depends critically on the electron drift velocity. Detailed analysis of the optical phonon increment as a function of phonon wavevector, electron-phonon coupling strength, electron temperature and drift velocity indicates that the electron drift in selectively doped AlAs/GaAs/AlAs and GaSb/InSb/GaAs quantum wells can generate coherent confined optical modes. Finally, we discuss nonlinear mechanisms which stabilize the increase of phonon population and lead to the steady state phonon generation.}, booktitle={Ultrafast Phenomena in Semiconductors VI}, publisher={SPIE}, author={Kim, Ki Wook and Komirenko, Sergiy M. and Kochelap, Viatcheslav A. and Stroscio, Michael A.}, editor={Tsen, Kong-Thon F. and Song, Jin-Joo and Jiang, HongxingEditors}, year={2002}, month={Jun} }
 @inproceedings{williams_hulfachor_kim_littlejohn_2002, title={Channel engineering in n-MOSFETs: scaling trends for hot electron injection and device degradation}, ISBN={0780333586}, url={http://dx.doi.org/10.1109/DRC.1996.546299}, DOI={10.1109/DRC.1996.546299}, abstractNote={Drain engineering has been the primary focus of efforts to overcome reliability trade-offs dictated by channel hot electron injection (CHEI) into the oxide in MOSFET devices. Comparatively few studies on channel, or vertical, engineering have been conducted, though recently there has been increased interest in its applications. In this study we employ a reliability simulation package to investigate the potential of channel engineering for future silicon technology by comparing scaling trends of CHEI and device sensitivity to the resulting distributions of induced interface damage for both Super-Steep-Retrograde (SSR) channel designs and more conventional (CONV) channel designs.}, booktitle={1996 54th Annual Device Research Conference Digest}, publisher={IEEE}, author={Williams, S.C. and Hulfachor, R.B. and Kim, K.W. and Littlejohn, M.A.}, year={2002}, month={Dec} }
 @article{komirenko_kim_kochelap_stroscio_2002, title={Confinement and amplification of acoustic waves in cubic heterostructures}, volume={65}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.65.155321}, DOI={10.1103/physrevb.65.155321}, abstractNote={We present the theory of acoustic phonon confinement in elastically anisotropic (cubic) quantum-well (QW) heterostructures grown in a direction of high symmetry. A general criterion for phonon confinement is derived. For Si/Si 0 . 5 Ge 0 . 5 /Si, Si/Ge/Si and AlAs/GaAs/AlAs QW heterostructures, dispersion curves are obtained, and displacement fields corresponding to the confined phonons are studied in detail. It is found that the confinement of acoustic phonons in these QW layers is strong in the subterahertz and terahertz frequency ranges. The resulting description of phonon confinement is applied to analyze the amplification of confined modes by the drift of the two-dimensional carriers as a function of the phonon frequency, the temperature, and the parameters of heterostructure. The calculation shows that the amplification coefficient of the confined phonons can exceed 10 3 cm - 1 for Si/Ge-based structures and 10 2 cm - 1 for AlAs/GaAs-based structures.}, number={15}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Komirenko, S. M. and Kim, K. W. and Kochelap, V. A. and Stroscio, M. A.}, year={2002}, month={Apr} }
 @article{komirenko_kim_kochelap_stroscio_2002, title={Confinement and amplification of terahertz acoustic phonons in cubic heterostructures}, volume={316-317}, ISSN={0921-4526}, url={http://dx.doi.org/10.1016/S0921-4526(02)00506-9}, DOI={10.1016/S0921-4526(02)00506-9}, abstractNote={A general criterion for phonon confinement is derived in the model of elastically anisotropic (cubic) media. The results are applied to the calculation of the dispersion curves of the confined phonons in Si/Si1−xGex/Si and AlAs/GaAs/AlAs heterostructures. For these structures, we show that the lowest-order phonon branches behave differently from those in the model of isotropic media. We have found that confinement is strong in the terahertz frequency range. For p-Si/SiGe/Si and n-AlAs/GaAs/AlAs quantum well heterostructures, we have studied the effect of amplification of confined high-frequency phonons by the drift of low-dimensional carriers. Two electron–phonon interaction mechanisms were taken into account: interaction via the deformation potential (p-SiGe and n-AlGaAs) and the piezoelectric interaction (n-AlGaAs). It was found that an amplification coefficient of the order of 102cm−1 for the AlGaAs heterostructures and 103cm−1 for the SiGe heterostructures can be obtained in spectrally-separated narrow amplification bands.}, journal={Physica B: Condensed Matter}, publisher={Elsevier BV}, author={Komirenko, S.M. and Kim, K.W. and Kochelap, V.A. and Stroscio, M.A.}, year={2002}, month={May}, pages={356–358} }
 @article{kiselev_kim_yablonovitch_2002, title={Designing a heterostructure for the quantum receiver}, volume={80}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1472480}, DOI={10.1063/1.1472480}, abstractNote={In this letter, we develop optimal parameters for a structure which is suitable for the realization of a coherent quantum receiver. Conditions including predefined photon wavelength, strain, small Zeeman splitting of the electron levels, and large Zeeman effect for quantum-confined light holes are satisfied simultaneously for the structure based on the InGaAsP solid solutions. We are able to achieve designs with wavelengths of 1.3 and 1.55 μm that are desirable for optoelectronic applications.}, number={16}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kiselev, A. A. and Kim, K. W. and Yablonovitch, E.}, year={2002}, month={Apr}, pages={2857–2859} }
 @article{kiselev_kim_yablonovitch_2002, title={Designing heterostructures with predefined value of light-hole g factor for coherent solid-state quantum receiver}, volume={13}, ISSN={1386-9477}, url={http://dx.doi.org/10.1016/S1386-9477(02)00204-7}, DOI={10.1016/S1386-9477(02)00204-7}, abstractNote={In this paper, we give a consistent theoretical analysis of the in-plane Zeeman effect for quantum-confined light holes and evaluate possibilities to design structures with desired property of large g factor for these valence states. Numerical example is given for the technologically important InGaAs/InP both lattice-matched and strained heterosystems suitable for 1.3 and 1.55μm optoelectronic applications.}, number={2-4}, journal={Physica E: Low-dimensional Systems and Nanostructures}, publisher={Elsevier BV}, author={Kiselev, A.A and Kim, K.W and Yablonovitch, E}, year={2002}, month={Mar}, pages={630–633} }
 @article{glavin_kochelap_linnik_kim_stroscio_2002, title={Generation of high-frequency coherent acoustic phonons in superlattices under hopping transport. I. Linear theory of phonon instability}, volume={65}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.65.085303}, DOI={10.1103/physrevb.65.085303}, abstractNote={In this work we consider the theory of high-frequency phonon generation in a weakly coupled doped semiconductor superlattice. Electric bias, applied to such a superlattice, destroys the electron minibands, creates electron states localized in the individual quantum wells, and forms population inversion between these states. An electric current occurs due to the phonon-induced interwell hops. We show that under such conditions the electric current produces a phonon instability: populations of phonon modes propagating almost collinearly with the superlattice axis increase exponentially in time. It is demonstrated that the population growth increment can be as high as several times 10 8 s - 1 . and considerably exceeds the internal phonon scattering rates. Also discussed are effects influencing the increment, such as a screening of the electron-phonon interaction and a modification of the phonon spectrum in superlattices.}, number={8}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Glavin, B. A. and Kochelap, V. A. and Linnik, T. L. and Kim, K. W. and Stroscio, M. A.}, year={2002}, month={Jan} }
 @article{glavin_kochelap_linnik_kim_stroscio_2002, title={Generation of high-frequency coherent acoustic phonons in superlattices under hopping transport. II. Steady-state phonon population and electric current in generation regime}, volume={65}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.65.085304}, DOI={10.1103/physrevb.65.085304}, abstractNote={For electrically biased superlattices exhibiting the effect of phonon instability (see paper I), we analyze the nonlinear problem of high-frequency acoustic phonon generation. We develop a theory treating self-consistently phonon generation and electron transport through the superlattice. We find that the dominant mechanism associated with the steady-state generation regime is electron heating caused by the nonequilibrium phonons. It is shown that under the generation regime the spectral distribution of phonons is extremely narrow, and that the generated power density can be as high as ${10}^{6} \mathrm{W}/{\mathrm{m}}^{2}$ for terahertz phonons. The electric current is controlled by the nonequilibrium phonons, and is higher by an order of magnitude than that under subthreshold conditions. In addition, we conclude that for the real superlattice structures the threshold condition is likely to be reached for the miniband-edge phonons having zero group velocity and negligible radiation losses.}, number={8}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Glavin, B. A. and Kochelap, V. A. and Linnik, T. L. and Kim, K. W. and Stroscio, M. A.}, year={2002}, month={Jan} }
 @article{barry_kim_kochelap_2002, title={Hot electrons in group-III nitrides at moderate electric fields}, volume={80}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1464666}, DOI={10.1063/1.1464666}, abstractNote={By the use of the Monte Carlo method, we studied the distribution function and the basic characteristics of hot electrons in InN, GaN, and AlN under moderate electric fields. We found that in relatively low fields (of the order of kV/cm) the optical phonon emission dominates in the electron kinetics. This strongly inelastic process gives rise to a spindle-shaped distribution function and an extended portion of a quasisaturation of the current–voltage (I–V) characteristics (the streaming-like regime). Formation of this regime is induced by a suppression of the electron spreading over the momenta perpendicular to the electric field. We prove that this is a universal character of the hot electron behavior for all three nitrides. The effects can be detected by the measurement of the I–V characteristics, or the thermopower of hot electrons in the transverse direction.}, number={13}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Barry, E. A. and Kim, K. W. and Kochelap, V. A.}, year={2002}, month={Apr}, pages={2317–2319} }
 @article{komirenko_kim_kochelap_zavada_2002, title={Laterally doped heterostructures for III–N lasing devices}, volume={81}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1527985}, DOI={10.1063/1.1527985}, abstractNote={To achieve a high-density electron-hole plasma in group-III nitrides for efficient light emission, we propose a planar two-dimensional (2D) p-i-n structure that can be formed in the quantum well layers due to efficient activation of donors and acceptors in the laterally, selectively doped barriers. We show that strongly nonequilibrium 2D electron-hole plasma with density above 1012 cm−2 can be realized in the i region of the laterally biased p-i-n structure, enabling the formation of interband population inversion and stimulated emission from such a lateral current pumped emitter (LACE). We suggest that implementation of the lateral p-i-n structures provides an efficient way of utilizing potential-profile-enhanced doping of superlattices and quantum wells for electric pumping of nitride-based lasers.}, number={24}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Komirenko, S. M. and Kim, K. W. and Kochelap, V. A. and Zavada, J. M.}, year={2002}, month={Dec}, pages={4616–4618} }
 @inproceedings{kim_komirenko_stroscio_kochelap_2002, title={Optical phonons in wurtzite and cubic structures}, ISBN={0780374320}, url={http://dx.doi.org/10.1109/ISDRS.2001.984578}, DOI={10.1109/ISDRS.2001.984578}, abstractNote={Optical phonons play a crucial role in polar semiconductors due to their strong interaction with electrons. The phonons and electron-phonon interaction have been investigated primarily in cubic materials due to relative simplicity of the phonon spectra in these optically isotropic materials. Recent interest in group III-nitrides, which usually crystallize in a hexagonal wurtzite structure, as well as the needs of contemporary technologies in nanoscale sources of high-frequency oscillations have brought up a number of additional questions related to phonon physics in solid state devices. In this abstract, we summarize the main differences between the optical phonon spectra in wurtzite and cubic structures and point to the significance of the electron-phonon interaction strength for a number of phonon-related problems and applications.}, booktitle={2001 International Semiconductor Device Research Symposium. Symposium Proceedings (Cat. No.01EX497)}, publisher={IEEE}, author={Kim, K.W. and Komirenko, S.M. and Stroscio, M.A. and Kochelap, V.A.}, year={2002}, month={Nov} }
 @article{stroscio_dutta_kahn_kim_komirenko_2002, title={Phonons in nanostructures: device applications}, volume={316-317}, ISSN={0921-4526}, url={http://dx.doi.org/10.1016/S0921-4526(02)00418-0}, DOI={10.1016/s0921-4526(02)00418-0}, abstractNote={This review highlights the utility of the dielectric and elastic continuum models for describing phonons in nanostructures. The properties of confined, interface and propagating modes in wurtzite quantum-confined structures may be described theoretically in terms of the dielectric continuum and Loudon's model for uniaxial semiconductors. Moreover, dimensionally confined acoustic phonon modes in nanostructures and carbon nanotubes may be described in terms of the elastic continuum models.}, journal={Physica B: Condensed Matter}, publisher={Elsevier BV}, author={Stroscio, M. and Dutta, M. and Kahn, D. and Kim, K.W. and Komirenko, S.}, year={2002}, month={May}, pages={8–11} }
 @article{song_kim_2002, title={Spin relaxation of conduction electrons in bulk III-V semiconductors}, volume={66}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.66.035207}, DOI={10.1103/physrevb.66.035207}, abstractNote={The spin relaxation time of conduction electrons through the Elliot-Yafet, D'yakonov-Perel, and Bir-Aronov-Pikus mechanisms is calculated theoretically for bulk GaAs, GaSb, InAs, and InSb of both n and p type. The relative importance of each spin relaxation mechanism is compared, and diagrams showing the dominant mechanism are constructed as a function of the temperature and impurity concentration. Our approach is based upon theoretical calculations of the momentum relaxation rate, and allows one to understand the interplay between various factors affecting the spin relaxation over a broad range of temperature and impurity concentration.}, number={3}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Song, Pil Hun and Kim, K. W.}, year={2002}, month={Jul} }
 @article{semenov_borysenko_kim_2002, title={Spin-phase relaxation of two-dimensional holes localized in a fluctuating potential}, volume={66}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.66.113302}, DOI={10.1103/physrevb.66.113302}, abstractNote={We investigate a mechanism of spin phase relaxation for holes localized by an in-plane potential fluctuation in a quantum well. Dephasing is caused by the hole spin precession in a magnetic field with a fluctuation in the transverse g factor linked to the depth and the shape of localizing potential. The mechanism can be recognized by the linear dependences on magnetic field and the quadratic dependence on quantum well width. Quantitative analyses show the importance of this relaxation mechanism for deep fluctuative states of holes.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Semenov, Y. G. and Borysenko, K. N. and Kim, K. W.}, year={2002}, month={Sep} }
 @article{lee_yu_kim_stroscio_dutta_2002, title={Transmission of longitudinal optical phonons through a barrier in uniaxial crystals}, volume={65}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.65.153315}, DOI={10.1103/physrevb.65.153315}, abstractNote={Transmission of longitudinal optical (LO) phonons in double heterostructures with uniaxial anisotropy is investigated within a dielectric continuum model. When LO-like phonons are generated in the left semi-infinite layer, their transmission probability through a barrier to the right semi-infinite layer is calculated. In x Ga 1 - x N/GaN/In x Ga 1 - x N and GaN/Al x Ga 1 - x N/GaN systems are considered for numerical calculations. In contrast to the isotropic case, where there is no transmission, it is shown that the propagation probability could be significant with only about 1% anisotropy. The propagation probability of phonons is found to increase with increasing wavelength of the LO-like phonon for a given harrier width.}, number={15}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Lee, B. C. and Yu, SeGi and Kim, K. W. and Stroscio, M. A. and Dutta, M.}, year={2002}, month={Apr} }
 @article{glavin_kochelap_linnik_kim_stroscio_2002, title={Voltage-controlled generation of high-frequency coherent acoustic phonons in superlattices}, volume={12}, ISSN={1386-9477}, url={http://dx.doi.org/10.1016/S1386-9477(01)00330-7}, DOI={10.1016/S1386-9477(01)00330-7}, abstractNote={Abstract We demonstrate that doped superlattices in the hopping conduction regime can be used for efficient generation of high-frequency coherent acoustic phonons. The phonons that can be generated in actual finite-length superlattice structures lay at the edge of the phonon miniband and have vanishingly small radiation losses. This causes onset of the phonon generation in a relatively narrow range of Stark splitting (or electric bias) which is complemented by a peak of the current–voltage characteristic of superlattice.}, number={1-4}, journal={Physica E: Low-dimensional Systems and Nanostructures}, publisher={Elsevier BV}, author={Glavin, B.A. and Kochelap, V.A. and Linnik, T.L. and Kim, K.W. and Stroscio, M.A.}, year={2002}, month={Jan}, pages={458–461} }
 @article{komirenko_kim_demidenko_kochelap_stroscio_2001, title={Amplification of transverse acoustic phonons in quantum well heterostructures with piezoelectric interaction}, volume={90}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1402145}, DOI={10.1063/1.1402145}, abstractNote={We have analyzed amplification of transverse phonons confined in quantum well (QW) heterostructures through piezoelectric electron–phonon interaction with drifting electrons. It was found that this mechanism of interaction couples the low-dimensional electrons and the shear-horizontal (SH) confined phonons. We have studied the electrostatic potential accompanying the SH waves and found that efficient interaction can be achieved for the lowest antisymmetric SH phonon branch in a narrow band of phonon frequencies. For AlGaAs QWs the amplification coefficient was calculated to be on the order of 100 cm−1 in the sub-THz phonon frequency range. These results suggest an electrical method for coherent phonon generation in the technologically well-developed AlGaAs QW heterostructures.}, number={8}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Komirenko, S. M. and Kim, K. W. and Demidenko, A. A. and Kochelap, V. A. and Stroscio, M. A.}, year={2001}, month={Oct}, pages={3934–3941} }
 @article{komirenko_kim_stroscio_dutta_2001, title={Applicability of the Fermi golden rule and the possibility of low-field runaway transport in nitrides}, volume={13}, ISSN={0953-8984 1361-648X}, url={http://dx.doi.org/10.1088/0953-8984/13/28/306}, DOI={10.1088/0953-8984/13/28/306}, abstractNote={We investigated electron transport characteristics of wide-band polar semi-conductors with intermediate strength of the electron–phonon interaction. Electron energy loss to the lattice was calculated as a function of electron velocity for various materials in the frameworks of (a) a perturbative approach based on the calculation of scattering rates from Fermi's golden rule and (b) a non-perturbative approach based on the path-integral formalism of Thornber and Feynman. Our results suggest that the standard perturbative treatment can be applied to GaN and AlN despite the relatively strong electron–phonon coupling in this material system, with intercollision times of the order of the period of the phonon oscillation. Our findings also indicate the possibility for unique long-distance runaway transport in nitrides which may occur at the pre-threshold electric fields. The polaron ground-state energy and effective masses are calculated for GaN and AlN as well as for GaAs and Al2O3. An expression for the Fröhlich coupling constant for wurtzites is derived.}, number={28}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Komirenko, S M and Kim, K W and Stroscio, M A and Dutta, M}, year={2001}, month={Jun}, pages={6233–6246} }
 @article{stroscio_dutta_kahn_kim_2001, title={Continuum model of optical phonons in a nanotube}, volume={29}, ISSN={0749-6036}, url={http://dx.doi.org/10.1006/spmi.2001.0980}, DOI={10.1006/spmi.2001.0980}, abstractNote={The properties of nanotubes are of intense current interest due, in part, to the discovery of the carbon nanotube. In this paper, the optical phonons are modeled for a nanotube by treating the nanotube as a continuum medium. A quantization prescription is applied to facilitate the first determination of the quantum-mechanical normalizations of selected optical phonon modes. It is shown that normalization of the lowest azimuthal mode may be determined analytically. The deformation potentials describing carrier optical-phonon scattering are readily determined from these normalized continuum modes.}, number={6}, journal={Superlattices and Microstructures}, publisher={Elsevier BV}, author={Stroscio, Michael A. and Dutta, Mitra and Kahn, Daniel and Kim, Ki Wook}, year={2001}, month={Jun}, pages={405–409} }
 @article{kosaka_kiselev_baron_kim_yablonovitch_2001, title={Electron g factor engineering in III-V semiconductors for quantum communications}, volume={37}, ISSN={0013-5194}, url={http://dx.doi.org/10.1049/el:20010314}, DOI={10.1049/el:20010314}, abstractNote={An entanglement-preserving photodetector converts photon polarisation to electron spin. Up and down spin must respond equally to oppositely polarised photons, creating a requirement for degenerate spin energies. g/sub e//spl sime/0, for electrons. The authors present a plot of g/sub e/ factor against lattice constant, analogous to bandgap against lattice constant, that can be used for g factor engineering of III-V alloys and quantum wells.}, number={7}, journal={Electronics Letters}, publisher={Institution of Engineering and Technology (IET)}, author={Kosaka, H. and Kiselev, A.A. and Baron, F.A. and Kim, Ki Wook and Yablonovitch, E.}, year={2001}, pages={464} }
 @article{komirenko_kim_kochelap_fedorov_stroscio_2001, title={Generation of coherent confined LO phonons under the drift of two-dimensional electrons}, volume={63}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.63.165308}, DOI={10.1103/physrevb.63.165308}, abstractNote={This paper addresses the effect of generation of confined LO phonons by drifting electrons in quantum wells. We have obtained a general formula for the phonon increment as a function of the phonon wave vector, the electron drift velocity, and parameters of the structure. The kinetic parameters of the drifting electrons are estimated by using momentum and energy balance equations for electron scattering by the confined optical phonons. We have performed numerical estimates of the phonon increment, as well as the phonon lifetimes, and found that AlAs/GaAs/AlAs and GaSb/InSb/GaSb quantum well structures with high drift velocities can demonstrate the effect of generation of the coherent confined optical modes. Essentially, the phonon increment has a maximum as a function of the wave vector. This implies a strong selection of the generated phonon modes. We briefly discuss the nonlinear electron mechanism which stabilizes the increase of the phonon populations and provides for the steady-state phonon generation.}, number={16}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Komirenko, S. M. and Kim, K. W. and Kochelap, V. A. and Fedorov, I. and Stroscio, M. A.}, year={2001}, month={Apr} }
 @article{barry_kim_kochelap_2001, title={Group-III nitrides hot electron effects in moderate electric fields}, volume={228}, DOI={10.1002/1521-3951(200111)228:2<571::aid-pssb571>3.0.co;2-i}, abstractNote={We studied the distribution function and basic characteristics of hot electrons in InN, GaN and AlN under moderate electric fields, and found that in relatively low fields (of the order of kV/cm) the optical phonon emission dominates the electron kinetics. This strongly inelastic process gives rise to a spindle-shaped distribution function and an extended portion of quasi-saturation of the current-voltage characteristics (the streaming-like regime). We prove that this hot electron regime holds for all three nitrides. We suggest that the effects can be detected by the measurement of the I-V characteristics, or the thermopower of hot electrons in the transverse direction.}, number={2}, journal={Physica Status Solidi. B, Basic Solid State Physics}, author={Barry, E. A. and Kim, K. W. and Kochelap, V. A.}, year={2001}, pages={571–574} }
 @article{komirenko_kim_kochelap_stroscio_2001, title={High-field electron transport in nanoscale group-III nitride devices}, volume={228}, ISSN={["0370-1972"]}, DOI={10.1002/1521-3951(200111)228:2<593::aid-pssb593>3.0.co;2-2}, abstractNote={Focusing on the short-size group-III nitride heterostructures, we have developed a model which takes into account main features of transport of electrons injected into a polar semiconductor under high electric fields. The model is based on an exact analytical solution of Boltzmann transport equation. The electron velocity distribution over the device is analyzed at different fields and the basic characteristics of the high-field electron transport are obtained. The critical field for the runaway regime, when electron energies and velocities increase with distance which results in the average velocities higher than the peak velocity in bulk-like samples, is determined. We have found that the runaway electrons are characterized by a distribution function with population inversion. Different nitride-based small-size devices where this effect can have an impact on the device performance are considered.}, number={2}, journal={PHYSICA STATUS SOLIDI B-BASIC RESEARCH}, author={Komirenko, SM and Kim, KW and Kochelap, VA and Stroscio, MA}, year={2001}, month={Nov}, pages={593–597} }
 @article{kiselev_kim_yablonovitch_2001, title={In-plane light-holegfactor in strained cubic heterostructures}, volume={64}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.64.125303}, DOI={10.1103/physrevb.64.125303}, abstractNote={In the context of a proposed design of a solid-state receiver for quantum communications, we consider the Zeeman splitting of the light-hole states in strained cubic heterostructures with an in-plane external magnetic field. The choice of interband optical transitions that allows coherent transfer of photon polarization to electron spin suggests that the magnitude of corresponding g factor component will be a critically important quantity for the success of such devices. Our approach allows a straightforward calculation of this parameter and incorporates the quantum confinement, heterolayers composition, and strain effects on the g factor.}, number={12}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kiselev, A. A. and Kim, K. W. and Yablonovitch, E.}, year={2001}, month={Sep} }
 @article{dutta_alexson_bergman_nemanich_dupuis_kim_komirenko_stroscio_2001, title={Phonons in III–V nitrides: Confined phonons and interface phonons}, volume={11}, ISSN={1386-9477}, url={http://dx.doi.org/10.1016/S1386-9477(01)00217-X}, DOI={10.1016/S1386-9477(01)00217-X}, abstractNote={Phonons in III–V nitrides are examined experimentally for dimensionally confined systems and for alloys of InGaN with a view towards understanding the phonon modes of these systems. Results are compared with the predictions of Loudon's model for uniaxial semiconductors. The modes of the InGaN system are compared with those of the AlGaN ternary alloy. The first Raman measurements of interface phonons in binary GaN–AlN superlattices are presented.}, number={2-3}, journal={Physica E: Low-dimensional Systems and Nanostructures}, publisher={Elsevier BV}, author={Dutta, M and Alexson, D and Bergman, L and Nemanich, R.J and Dupuis, R and Kim, K.W and Komirenko, S and Stroscio, M}, year={2001}, month={Oct}, pages={277–280} }
 @article{kahn_kim_stroscio_2001, title={Quantized vibrational modes of nanospheres and nanotubes in the elastic continuum model}, volume={89}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.1356429}, DOI={10.1063/1.1356429}, abstractNote={The properties of nanoscale spheres and tubes are of recent interest due to the discovery of the fullerene molecule and the carbon nanotube. These carbon structures can be modeled as nanoscale spherical or cylindrical shells. In this article, these nanostructures are treated in the thin shell approximation with the elastic properties taken to be those of the graphene sheet. A quantization prescription is applied to the classical elastic modes to facilitate the first calculations of the quantum-mechanical normalizations of selected modes. These modes are shown to be amenable to the study of electron-phonon interactions. Indeed, electron-phonon interaction Hamiltonians are derived. Moreover, it is shown for such a tube of finite length that the electron-phonon interaction strength depends on the axial position. As a special case it is shown that the dispersion relation for the clamped tube depends on the length of the tube. In this article we consider both the vibrational frequencies and the mode quantization for both spherical shell and the nanotube using realistic material parameters.}, number={9}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kahn, Daniel and Kim, K. W. and Stroscio, Michael A.}, year={2001}, month={May}, pages={5107–5111} }
 @article{komirenko_kim_kochelap_stroscio_2001, title={Runaway effects in nanoscale group-III nitride semiconductor structures}, volume={64}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.64.113207}, DOI={10.1103/physrevb.64.113207}, abstractNote={We have revisited the problem of electron runaway in strong electric fields in polar semiconductors focusing on nanoscale group-III nitride structures. By developing a transport model that accounts for the main features of electrons injected in short devices under high electric fields, we have investigated the electron distribution as a function of electron momenta and coordinates. Runaway transport is analyzed in detail. The critical field of this regime is determined for InN, GaN, and AlN. We found that the transport in the nitrides is always dissipative (i.e., no ballistic transport). For the runaway regime, however, the electrons increase their velocities with distance, which results in average velocities higher than the peak velocity in bulklike samples. We have demonstrated that the runaway electrons are characterized by a distribution function exhibiting a population inversion.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Komirenko, S. M. and Kim, K. W. and Kochelap, V. A. and Stroscio, M. A.}, year={2001}, month={Aug} }
 @article{kiselev_kim_2001, title={T-shaped ballistic spin filter}, volume={78}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1347023}, DOI={10.1063/1.1347023}, abstractNote={We propose a semiconductor structure that can filter electron spin without using external magnetic fields. The structure consists of a T-shaped quasi-one-dimensional channel and an electrode placed near the channel intersection to control the spin-orbit interaction for electrons. Our calculations demonstrate that the proposed device can redirect electrons with opposite spins from an unpolarized source to left and right output leads, respectively, and, thus, serve as a spin filter. When the incident electron energy is in resonance with the quasilocalized zero-dimensional states at the intersection, polarization of the transmitted fluxes approaches 100%.}, number={6}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kiselev, A. A. and Kim, K. W.}, year={2001}, month={Feb}, pages={775–777} }
 @article{komirenko_kim_demidenko_kochelap_stroscio_2000, title={Cerenkov generation of high-frequency confined acoustic phonons in quantum wells}, volume={76}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.126195}, DOI={10.1063/1.126195}, abstractNote={We analyze the Cerenkov emission of high-frequency confined acoustic phonons by drifting electrons in a quantum well. We find that the electron drift can cause strong phonon amplification (generation). A general formula for the gain coefficient α is obtained as a function of the phonon frequency and the structure parameters. The gain coefficient increases sharply in the short-wave region. For the example of a Si/SiGe/Si device, it is shown that the amplification coefficients of the order of hundreds of cm−1 can be achieved in the subterahertz frequency range.}, number={14}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Komirenko, S. M. and Kim, K. W. and Demidenko, A. A. and Kochelap, V. A. and Stroscio, M. A.}, year={2000}, month={Apr}, pages={1869–1871} }
 @article{komirenko_kim_kochelap_fedorov_stroscio_2000, title={Coherent optical phonon generation by the electric current in quantum wells}, volume={77}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.1334653}, DOI={10.1063/1.1334653}, abstractNote={This letter addresses the effect of generation of confined LO phonons by drifting electrons in quantum wells. We have derived a general formula for the phonon increment as a function of phonon wave vector, electron drift velocity, and structure parameters. Numerical estimates of the phonon increment and the phonon lifetimes have shown that AlAs/GaAs/AlAs and GaSb/InSb/GaSb quantum well structures can demonstrate the effect of coherent LO phonon generation by the electric current.}, number={25}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Komirenko, S. M. and Kim, K. W. and Kochelap, V. A. and Fedorov, I. and Stroscio, M. A.}, year={2000}, month={Dec}, pages={4178–4180} }
 @article{komirenko_kim_stroscio_dutta_2000, title={Energy-dependent electron scattering via interaction with optical phonons in wurtzite crystals and quantum wells}, volume={61}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.61.2034}, DOI={10.1103/physrevb.61.2034}, abstractNote={A formalism for the calculation of the scattering rate in wurtzite-type crystals and quantum wells (QW's) is developed taking into account features of the optical phonon spectra in an optically anisotropic medium. The electron-scattering rate due to the interaction with infrared/Raman-active polar optical phonons in GaN, bulk material, and heterostructures, is investigated. To determine the dependence of scattering rate on optical anisotropy and dimensionally induced transformation of the phonon spectra, three cases are considered: (a) bulk material with different orientations of the electron wave vector with respect to the optical axis; (b) a system in which bulk phonons interact with electrons confined in a QW; and (c) free-standing and embedded QW's where the effects of confinement of both electron and phonon subsystems are taken into account. It is found that the scattering rate depends weakly on the initial orientation of the electron wave vector. Exceptions are the energy intervals which correspond to the threshold values for emission of both TO-like and LO-like bulk phonons. Our results reveal a complex and strong dependence of the electron-scattering rate on the dispersion of a particular mode. Moreover, this dependence is found to be the main factor which determines electron-phonon scattering in wurtzite heterostructures, in particular, through the relation between phonon phase and group velocities. For the optically anisotropic media considered, the effect of spatial localization of the phonon modes on the scattering rate is found to be as strong as the effect of electron confinement.}, number={3}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Komirenko, S. M. and Kim, K. W. and Stroscio, M. A. and Dutta, M.}, year={2000}, month={Jan}, pages={2034–2040} }
 @article{williams_kim_holton_2000, title={Ensemble Monte Carlo study of channel quantization in a 25-nm n-MOSFET}, volume={47}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.870564}, DOI={10.1109/16.870564}, abstractNote={We develop a self-consistent, ensemble Monte Carlo device simulator that is capable of modeling channel carrier quantization and polysilicon gate depletion in nanometer-scale n-MOSFETs. A key feature is a unique bandstructure expression for quantized electrons. Carrier quantization and polysilicon depletion are examined against experimental capacitance-voltage (C-V) data. Calculated drain current values are also compared with measured current-voltage data for an n-MOSFET with an effective channel length (L/sub eff/) of 90 nm. Finally, the full capabilities of the Monte Carlo simulator are used to investigate the effects of carrier confinement in a L/sub eff/=25 nm n-MOSFET. In particular, the mechanisms affecting the subband populations of quantized electrons in the highly nonuniform channel region are investigated. Simulation results indicate that the occupation levels in the subbands are a strong function of the internal electric field configurations and two-dimensional (2-D) carrier scattering.}, number={10}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Williams, S.C. and Kim, K.W. and Holton, W.C.}, year={2000}, pages={1864–1872} }
 @article{jeon_sanders_kim_littlejohn_2000, title={Exciton binding energies in GaN/AlxGa1−xN pseudomorphic quantum wells}, volume={27}, ISSN={0749-6036}, url={http://dx.doi.org/10.1006/spmi.1999.0819}, DOI={10.1006/spmi.1999.0819}, abstractNote={Abstract Interband transitions of pseudomorphic GaN/ Al x Ga 1 −  x N quantum wells are analysed theoretically with respect to the piezoelectric field utilizing a 6  ×  6 Rashba–Sheka–Pikus (RSP) Hamiltonian. Band structure modifications due to the built-in Stark effect explain a shift of the emission peak in GaN/ Al 0.15 Ga 0.85 N of up to 400 meV. Quantum well exciton binding energies are calculated by the variational method and are discussed in terms of spatial separation of electrons and holes by the built-in electric field, as well as the interaction between valence subbands.}, number={1}, journal={Superlattices and Microstructures}, publisher={Elsevier BV}, author={Jeon, J.-B and Sanders, G.D and Kim, K.W and Littlejohn, M.A}, year={2000}, month={Jan}, pages={53–58} }
 @article{komirenko_kim_demidenko_kochelap_stroscio_2000, title={Generation and amplification of sub-THz coherent acoustic phonons under the drift of two-dimensional electrons}, volume={62}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.62.7459}, DOI={10.1103/physrevb.62.7459}, abstractNote={This paper addresses the \ifmmode \check{C}\else \v{C}\fi{}erenkov emission of high-frequency confined acoustic phonons by drifting electrons in a quantum well. We have found that the electron drift can cause strong phonon amplification (generation). The spectra of the confined modes are calculated and their confinement properties are analyzed. The spectra consist of a set of branches, and for each branch, the confinement effect increases considerably when the phonon wave vector increases. We have studied the coupling between electrons and confined modes and proved that the coupling is a nonmonotonous function of the wave vector for each of the phonon branches. We have obtained a general formula for the gain coefficient as a function of the phonon frequency and the structure parameters. For each of the branches, the amplification takes place in a spectrally separated and quite narrow amplification band in the high-frequency range. For the example of p-doped Si/SiGe/Si heterostructures it is shown that the amplification coefficients of the order of hundreds of ${\mathrm{cm}}^{\ensuremath{-}1}$ can be achieved in the sub-THz frequency range.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Komirenko, S. M. and Kim, K. W. and Demidenko, A. A. and Kochelap, V. A. and Stroscio, M. A.}, year={2000}, month={Sep}, pages={7459–7469} }
 @article{collins_kim_holton_sierzputowska-gracz_stejskal_2000, title={NMR quantum computation with indirectly coupled gates}, volume={62}, ISSN={1050-2947 1094-1622}, url={http://dx.doi.org/10.1103/PhysRevA.62.022304}, DOI={10.1103/PhysRevA.62.022304}, abstractNote={An NMR realization of a two-qubit quantum gate which processes quantum information indirectly via couplings to a spectator qubit is presented in the context of the Deutsch-Jozsa algorithm. This enables a successful comprehensive NMR implementation of the Deutsch-Jozsa algorithm for functions with three argument bits and demonstrates a technique essential for multi-qubit quantum computation.}, number={2}, journal={Physical Review A}, publisher={American Physical Society (APS)}, author={Collins, David and Kim, K. W. and Holton, W. C. and Sierzputowska-Gracz, H. and Stejskal, E. O.}, year={2000}, month={Jul} }
 @inbook{holten_hauser_kim_lynch_2000, title={Overview of semiconductor devices}, booktitle={Handbook of semiconductor manufacturing technology}, publisher={New York: Marcel Dekker}, author={Holten, W. C. and Hauser, J. R. and Kim, K. W. and Lynch, W. T.}, editor={Y. Nishi and Doering, R.Editors}, year={2000} }
 @inproceedings{bergman_dutta_kim_klemens_komirenko_stroscio_2000, title={Phonons, electron-phonon interactions, and phonon-phonon interactions in III-V nitrides}, url={http://dx.doi.org/10.1117/12.381450}, DOI={10.1117/12.381450}, abstractNote={Fundamental properties of phonons in III-V nitrides are examined with a view toward understanding processes important in the operation of III-V nitride devices. Firstly, confined, interface and propagating modes in wurtzite quantum wells are described in terms of Loudon's model for uniaxial semiconductors and the dielectric continuum model. Basic properties of the phonon modes and carrier-phonon interactions are considered in the basis of this treatment of dimensionally-confined phonons in wurtzite structures. A key feature of these phonon modes is their enhanced dispersion and its origin from the non-isotropic nature of the wurtzites. As will be discussed, this dispersion has important consequences for phonon propagation and phonon energy spectra. Secondly, the second-order phonon decay process of combined point defect scattering and anharmonic decay is examined as a means of estimating line broadening associated with the decay of phonons in III-V nitrides of wurtzite structure containing point defects. Thirdly, an analysis of Raman linewidths measured for AlN and GaN wurtzites is made to estimate phonon lifetimes.}, booktitle={Ultrafast Phenomena in Semiconductors IV}, publisher={SPIE}, author={Bergman, Leah and Dutta, Mitra and Kim, Ki Wook and Klemens, Paul G. and Komirenko, Sergiy M. and Stroscio, Michael A.}, editor={Tsen, Kong-Thon F. and Song, Jin-JooEditors}, year={2000}, month={Mar} }
 @article{kiselev_kim_2000, title={Progressive suppression of spin relaxation in two-dimensional channels of finite width}, volume={61}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.61.13115}, DOI={10.1103/physrevb.61.13115}, abstractNote={We have investigated spatiotemporal kinetics of electron spin polarization in a semiconductor narrow two-dimensional (2D) strip and explored the ability to manipulate spin relaxation. Information about the conduction electron spin and mechanisms of spin rotation is incorporated into a Monte Carlo transport simulation program. A model problem, involving linear-in-$k$ splitting of the conduction band responsible for the D'yakonov-Perel' mechanism of spin relaxation in the zinc-blende semiconductors and heterostructures, is solved numerically to yield the decay of spin polarization of an electron ensemble in the 2D channel of finite width. For very wide channels, a conventional 2D value of spin relaxation is obtained. With decreasing channel width, the relaxation time increases rapidly by orders of magnitude. Surprisingly, the crossover point between 2D and quasi-1D behavior is found to be at tens of electron mean-free paths. Thus, classically wide channels can effectively suppress electron spin relaxation.}, number={19}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kiselev, A. A. and Kim, K. W.}, year={2000}, month={May}, pages={13115–13120} }
 @article{sanders_kim_holton_2000, title={Scalable solid-state quantum computer based on quantum dot pillar structures}, volume={61}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.61.7526}, DOI={10.1103/physrevb.61.7526}, abstractNote={We investigate an optically driven quantum computer based on electric dipole transitions within coupled single-electron quantum dots. Our quantum register consists of a free-standing n-type pillar containing a series of pairwise coupled asymmetric quantum dots, each with a slightly different energy structure, and with grounding leads at the top and bottom of the pillar. Asymmetric quantum wells confine electrons along the pillar axis, and a negatively biased gate wrapped around the center of the pillar allows for electrostatic confinement in the radial direction. We self-consistently solve coupled Schr\"odinger and Poisson equations and develop a design for a three-qubit quantum register. Our results indicate that a single gate electrode can be used to localize a single electron in each of the quantum dots. Adjacent dots are strongly coupled by electric dipole-dipole interactions arising from the dot asymmetry, thus enabling rapid computation rates. The dots are tailored to minimize dephasing due to spontaneous emission and phonon scattering and to maximize the number of computation cycles. The design is scalable to a large number of qubits.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Sanders, G. D. and Kim, K. W. and Holton, W. C.}, year={2000}, month={Mar}, pages={7526–7535} }
 @article{kiselev_kim_2000, title={Suppression of Dyakonov-Perel spin relaxation in 2D channels of finite width}, volume={221}, ISSN={["0370-1972"]}, DOI={10.1002/1521-3951(200009)221:1<491::aid-pssb491>3.0.co;2-i}, abstractNote={We have investigated spin-dependent transport in semiconductor narrow 2D channels and explored the possibility of suppressing spin relaxation. Our approach is based on a Monte Carlo transport model and incorporates information on conduction band electron spins and spin rotation mechanisms. Specifically, an ensemble of electrons experiencing multiple scattering events is simulated numerically to study the decay of electron spin polarization in channels of finite width due to the Dyakonov-Perel (DP) mechanism. We have identified different regimes of the spin relaxation in the 2D channels of finite width and established the dependencies of spin relaxation time on the width L and DP parameter ηDP. The most attractive regime for future spintronic applications is the regime of the suppressed spin relaxation with the relaxation time τS scaling as L—2.}, number={1}, journal={PHYSICA STATUS SOLIDI B-BASIC RESEARCH}, author={Kiselev, AA and Kim, KW}, year={2000}, month={Sep}, pages={491–494} }
 @article{kiselev_kim_stroscio_2000, title={Thermal conductivity of Si/Ge superlattices: A realistic model with a diatomic unit cell}, volume={62}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.62.6896}, DOI={10.1103/physrevb.62.6896}, abstractNote={This paper considers the effects of a realistic description of phonons in diamondlike semiconductors and their conversion on the abrupt heterointerfaces on the thermal conductivity of the superlattice (SL). Due to the much larger mass of Ge atoms in comparison to Si, the most probable acoustic phonons in Si layers at room temperature have no counterpart in Ge. In simplified models where Si and Ge are simulated by monatomic crystals with fitted parameters, this leads to the highly efficient trapping of high-energy acoustic phonons in Si layers and drastic reduction of the SL thermal conductivity. The proposed approach incorporates the optical branches and the effective conversion of the phonons at interfaces extends the temperature range for which the model is valid and thereby leads to corrections to predicted thermal conductivity.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kiselev, A. A. and Kim, K. W. and Stroscio, M. A.}, year={2000}, month={Sep}, pages={6896–6899} }
 @article{williams_kim_littlejohn_holton_1999, title={Analysis of hot-electron reliability and device performance in 80-nm double-gate SOI n-MOSFET's}, volume={46}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.777167}, DOI={10.1109/16.777167}, abstractNote={In this paper, we employ a comprehensive Monte Carlo-based simulation method to model hot-electron injection, to predict induced device degradation, and to simulate and compare the performance of two double-gate fully depleted silicon-on-insulator n-MOSFET's (one with a lightly-doped channel and one with a heavily-doped channel) and a similar lightly-doped single-gate design. All three designs have an effective channel length of 80 nm and a silicon layer thickness of 25 mm. Monte Carlo simulations predict a spatial retardation between the locations of peak hot-electron injection into the front and back oxides. Since the observed shift is a significant portion of the channel length, the retardation effect greatly influences induced degradation in otherwise well-designed SOI devices. This effect may signal an important consideration for sub-100-nm design strategy. Simulations were also conducted to compare transistor performance against a key figure of merit. Evaluation of reliability and performance results indicate that the double-gate design with a lightly doped channel offers the best tradeoff in immunity to hot-electron-induced degradation and performance.}, number={8}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Williams, S.C. and Kim, K.W. and Littlejohn, M.A. and Holton, W.C.}, year={1999}, pages={1760–1767} }
 @article{kiselev_kim_stroscio_1999, title={Calculational approach for the structure of electron and hole levels in quantum dots of varying shape}, volume={60}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.60.7748}, DOI={10.1103/physrevb.60.7748}, abstractNote={Another approach to the calculation of electron and hole states in quantum dots is proposed. It benefits from the particular choice of products of powers of Cartesian coordinates as a basis, since it is possible to evaluate all required matrix elements analytically for these systems. A variety of dot shapes in the presence of external electric fields can be analyzed conveniently. This approach provides a way to calculate quantum dot ensemble averages quickly and effectively.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kiselev, A. A. and Kim, K. W. and Stroscio, M. A.}, year={1999}, month={Sep}, pages={7748–7751} }
 @article{kiselev_kim_stroscio_1999, title={Computing carrier interactions with confined and excluded phonons in nanostructures of complex geometries}, volume={59}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.59.10212}, DOI={10.1103/physrevb.59.10212}, abstractNote={We provide a simple and highly effective procedure for calculating quantities such as electron scattering rates involving confined and excluded phonons for quantum wires of arbitrary geometry. This problem is particularly difficult to solve by the usual summation procedure as well as by alternative treatments proposed thus far. To demonstrate the strength of our approach, we produce exact analytical results in the case of a quantum well. As a numerical example, we consider a classic T-shaped structure with different sizes and radii of curvature at the intersections. We examine the possibility of manipulating structural characteristics such as electron-phonon scattering rates by making minor modifications to the quantum wire cross-sectional geometries.}, number={15}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kiselev, A. A. and Kim, K. W. and Stroscio, M. A.}, year={1999}, month={Apr}, pages={10212–10216} }
 @article{alexson_bergman_dutta_kim_komirenko_nemanich_lee_stroscio_yu_1999, title={Confined phonons and phonon-mode properties of III–V nitrides with wurtzite crystal structure}, volume={263-264}, ISSN={0921-4526}, url={http://dx.doi.org/10.1016/S0921-4526(98)01423-9}, DOI={10.1016/s0921-4526(98)01423-9}, abstractNote={Stimulated by the recent interest in the use of nitride-based III–V wurtzite structures for optoelectronic and electronic devices, this paper reports on the application of the Loudon model for uniaxial crystals to derive the Fröhlich interaction Hamiltonian as well as the electron–optical-phonon scattering rate in wurtzite crystals. This paper also presents experimental analyses of the mode behavior of phonons in wurtzite crystals.}, journal={Physica B: Condensed Matter}, publisher={Elsevier BV}, author={Alexson, D and Bergman, Leah and Dutta, Mitra and Kim, K.W and Komirenko, S and Nemanich, Robert J and Lee, B.C and Stroscio, Michael A and Yu, SeGi}, year={1999}, month={Mar}, pages={510–513} }
 @article{komirenko_kim_stroscio_dutta_1999, title={Dispersion of polar optical phonons in wurtzite quantum wells}, volume={59}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.59.5013}, DOI={10.1103/physrevb.59.5013}, abstractNote={Dispersion relations for polar optical phonon modes in wurtzite quantum wells (QW's) are obtained in the framework of the dielectric continuum model. It is found that anisotropy of the dielectric medium causes a number of qualitative peculiarities in the phonon spectra. Among these are the absence of the proper confinement for the oscillatory waves located in the QW, inversion of the order of symmetric and antisymmetric quasiconfined optical modes, formation of the finite energy intervals where such confined modes---which are found to be dispersive---can exist, penetration of the half-space phonons into the QW, etc. Some additional peculiarities, such as appearance of propagating modes, strong dispersion of long-wavelength half-space modes, and reduction of the number of interface modes, arise as a result of overlapping characteristic phonon frequencies of the surrounding material and the material of QW. Predicted phonon behavior leads to the conclusion that dependence of dielectric properties of ternary-binary low-dimensional wurtzite heterostructures on composition can serve as a powerful tool for the purposes of phonon spectrum engineering. In order to illustrate these results, the optical phonon spectra are calculated for an ${\mathrm{Al}}_{0.15}{\mathrm{Ga}}_{0.85}\mathrm{N}/\mathrm{GaN}/{\mathrm{Al}}_{0.15}{\mathrm{Ga}}_{0.85}\mathrm{N} \mathrm{QW},$ an $\mathrm{AlN}/\mathrm{GaN}/\mathrm{AlN} \mathrm{QW},$ and for a $\mathrm{GaN}$ dielectric slab.}, number={7}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Komirenko, S. M. and Kim, K. W. and Stroscio, M. A. and Dutta, M.}, year={1999}, month={Feb}, pages={5013–5020} }
 @article{sanders_kim_holton_1999, title={Optically driven quantum-dot quantum computer}, volume={60}, ISSN={1050-2947 1094-1622}, url={http://dx.doi.org/10.1103/PhysRevA.60.4146}, DOI={10.1103/PhysRevA.60.4146}, abstractNote={We propose a design for a quantum computer that builds on n-type SET structures reported by Tarucha et al. (1996). Our design consists of an array of free standing pillars with source and drain electrodes at the top and bottom of the pillar and a stacked series of asymmetric GaAs/AlGaAs quantum wells arrayed along the axis. By applying a negative bias to the cylindrical gate electrode, carriers near the surface are depleted. The parabolic electrostatic potential provides confinement in the radial direction while bandgap discontinuities in the quantum wells provide confinement along the pillar axis. In operating as a quantum computer the source and drain are grounded and the number of electrons in each dot are set to one by adjusting the gate voltage. Qubits are encoded in the ground state and first excited state of the quantum dot electrons. The pillar array constitutes an ensemble of quantum computers that operate simultaneously.}, number={5}, journal={Physical Review A}, publisher={American Physical Society (APS)}, author={Sanders, G. D. and Kim, K. W. and Holton, W. C.}, year={1999}, month={Nov}, pages={4146–4149} }
 @article{komirenko_kim_kochelap_dutta_stroscio_1999, title={Phase instability and electron-assisted renormalization of acoustic phonon spectrum in free-standing quantum wires}, volume={263-264}, ISSN={0921-4526}, url={http://dx.doi.org/10.1016/S0921-4526(98)01253-8}, DOI={10.1016/s0921-4526(98)01253-8}, abstractNote={Abstract In this paper we consider the possibility of a Peierls phase transition for a system of one-dimensional electrons and acoustic phonons confined in a free-standing quantum wire (FSQWI). We assume that electrons and phonons are coupled via the deformation potential interaction. The dispersion relation for this system is derived taking into account the role of electrostatic effects. The Peierls phase transition to the state characterized by periodic lattice deformation (PLD) is obtained in the high-permittivity limit. The formalism developed in this paper facilitates investigation of the renormalized acoustic phonon spectrum and predicts the possibility of the Peierls transition in FSQWIs fabricated from semiconductor materials with large permittivity.}, journal={Physica B: Condensed Matter}, publisher={Elsevier BV}, author={Komirenko, S.M. and Kim, K.W. and Kochelap, V.A. and Dutta, Mitra and Stroscio, Michael A.}, year={1999}, month={Mar}, pages={522–525} }
 @article{jeon_sanders_kim_littlejohn_1999, title={Piezoelectric and excitonic effects on optical properties of pseudomorphically strained wurtzite GaN quantum well lasers}, number={162}, journal={Compound semiconductors 1998  (Institute of Physics conference series;  no. 162)}, publisher={Bristol; Philadelphia: Institute of Physics Pub.}, author={Jeon, J. B. and Sanders, G. D. and Kim, K. W. and Littlejohn, M. A.}, year={1999}, pages={37–42} }
 @article{sanders_kim_holton_1999, title={Quantum computing with complex instruction sets}, volume={59}, ISSN={1050-2947 1094-1622}, url={http://dx.doi.org/10.1103/PhysRevA.59.1098}, DOI={10.1103/PhysRevA.59.1098}, abstractNote={In most current quantum computers simple electromagnetic pulses implement computations using a minimal set of universal gates. We propose an approach in which quantum control techniques combined with flexible electromagnetic pulse shaping are used to replace several universal gates with a single instruction. We show that this complex instruction set approach can significantly reduce the time required to perform quantum computations.}, number={2}, journal={Physical Review A}, publisher={American Physical Society (APS)}, author={Sanders, G. D. and Kim, K. W. and Holton, W. C.}, year={1999}, month={Feb}, pages={1098–1101} }
 @article{belenky_dutta_b. gorfinkel_haddad_iafrate_kim_kisin_luryi_stroscio_sun_et al._1999, title={Tailoring of optical phonon modes in nanoscale semiconductor structures: role of interface-optical phonons in quantum-well lasers}, volume={263-264}, ISSN={0921-4526}, url={http://dx.doi.org/10.1016/S0921-4526(98)01410-0}, DOI={10.1016/S0921-4526(98)01410-0}, abstractNote={This paper discusses the concept of enhancing semiconductor laser performance through tailoring of scattering rates of confined polar-optical phonons. Studies of optically pumped intersubband scattering in coupled quantum-well lasers have demonstrated that interface-phonon-assisted transitions are important in such structures; furthermore, simple analytical expressions have been derived that indicate the importance of interface-phonon scattering in quantum-well lasers. These calculations reveal that the interface-phonon-assisted transitions are dominant for small quantum well dimensions of approximately 40 Å; such dimensions are typical of novel lasers including both the unipolar quantum cascade laser and the tunneling injection laser. Recent numerical calculations have confirmed these effects and have extended them to indicate how confined and interface phonons also affect critical laser properties such as optical gain. The application of confined phonon effects to intersubband lasers is one of the most important applications of confined-phonon physics to the present time.}, journal={Physica B: Condensed Matter}, publisher={Elsevier BV}, author={Belenky, Gregory and Dutta, Mitra and B. Gorfinkel, Vera and Haddad, George I. and Iafrate, G.J. and Kim, K.W. and Kisin, Mikhail and Luryi, Serge and Stroscio, Michael A. and Sun, J.P. and et al.}, year={1999}, month={Mar}, pages={462–465} }
 @article{kiselev_kim_ivchenko_1999, title={Zeeman effect in wurtzite-based and strained cubic heterostructures}, volume={215}, ISSN={["0370-1972"]}, DOI={10.1002/(sici)1521-3951(199909)215:1<235::aid-pssb235>3.0.co;2-s}, abstractNote={We investigate theoretically the Zeeman effect on the lowest confined subbands in wurtzite heterostructures. The powerful approach suggested recently for zincblende-based nanostructures is extended to a new symmetry class and analytical expressions are derived for the first time for the g-factors in the technologically important nitride-based quantum wells and AIIBVI heterostructures, in the framework of the quasi-cubical Kane model. In our calculation we make allowance for the strain in heterolayers and huge internal electric fields due to spontaneous polarization and lattice-constant mismatch between the compositional materials.}, number={1}, journal={PHYSICA STATUS SOLIDI B-BASIC RESEARCH}, author={Kiselev, AA and Kim, KW and Ivchenko, EL}, year={1999}, month={Sep}, pages={235–239} }
 @article{lu_holton_fenner_williams_kim_hartford_chen_roze_littlejohn_1998, title={A new device design methodology for manufacturability}, volume={45}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.661225}, DOI={10.1109/16.661225}, abstractNote={As future technology generations for integrated circuits continue to "shrink", TCAD tools must be made more central to manufacturing issues; thus, yield optimization and design for manufacturing (DFM) should be addressed integrally with performance and reliability when using TCAD during the initial product design. This paper defines the goals for DFM in TCAD simulations and outlines a formal procedure for achieving an optimized result (ODFM). New design of experiments (DOE), weighted least squares modeling and multiple-objective mean-variance optimization methods are developed as significant parts of the new ODFM procedure. Examples of designing a 0.18-/spl mu/m MOSFET device are given to show the impact of device design procedures on device performance distributions and sensitivity variance profiles.}, number={3}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Lu, J.-C. and Holton, W.C. and Fenner, J.S. and Williams, S.C. and Kim, K.W. and Hartford, A.H. and Chen, D. and Roze, K. and Littlejohn, M.A.}, year={1998}, month={Mar}, pages={634–642} }
 @article{collins_kim_holton_1998, title={Deutsch-Jozsa algorithm as a test of quantum computation}, volume={58}, ISSN={1050-2947 1094-1622}, url={http://dx.doi.org/10.1103/PhysRevA.58.R1633}, DOI={10.1103/PhysRevA.58.R1633}, abstractNote={A redundancy in the existing Deutsch-Jozsa quantum algorithm is removed and a refined algorithm, which reduces the size of the register and simplifies the function evaluation, is proposed. The refined version allows a simpler analysis of the use of entanglement between the qubits in the algorithm and provides criteria for deciding when the Deutsch-Jozsa algorithm constitutes a meaningful test of quantum computation.}, number={3}, journal={Physical Review A}, publisher={American Physical Society (APS)}, author={Collins, David and Kim, K. W. and Holton, W. C.}, year={1998}, month={Sep}, pages={R1633–R1636} }
 @article{yu_pevzner_kim_stroscio_1998, title={Electrophonon resonance in cylindrical quantum wires}, volume={58}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.58.3580}, DOI={10.1103/physrevb.58.3580}, number={7}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Yu, SeGi and Pevzner, V. B. and Kim, K. W. and Stroscio, Michael A.}, year={1998}, month={Aug}, pages={3580–3583} }
 @article{yu_kim_bergman_dutta_stroscio_zavada_1998, title={Long-wavelength optical phonons in ternary nitride-based crystals}, volume={58}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.58.15283}, DOI={10.1103/physrevb.58.15283}, abstractNote={Phonon modes in column-III--nitride ternary semiconductors are investigated theoretically within the modified random-element isodisplacement model. It is found that ${A}_{1}$ and ${E}_{1}$ branches of optical phonons in wurtzite ${\mathrm{Ga}}_{x}{\mathrm{Al}}_{1\ensuremath{-}x}\mathrm{N}$ and ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ exhibit one-mode behavior. This result is explained by the fact that atomic mass of nitrogen is much smaller than those of other atoms.}, number={23}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Yu, SeGi and Kim, K. W. and Bergman, Leah and Dutta, Mitra and Stroscio, Michael A. and Zavada, John M.}, year={1998}, month={Dec}, pages={15283–15287} }
 @article{sirenko_jeon_kim_littlejohn_1998, title={Optical gain, hole transport, intervalence band optical transitions in group III nitrides: Envelope function description}, volume={97}, number={34}, journal={Proceedings of the second symposium on III-V nitride materials and processes}, author={Sirenko, Y. and Jeon, J.B. and Kim, K.W. and Littlejohn, M.A.}, year={1998}, pages={177–188} }
 @article{lee_kim_stroscio_dutta_1998, title={Optical-phonon confinement and scattering in wurtzite heterostructures}, volume={58}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.58.4860}, DOI={10.1103/physrevb.58.4860}, abstractNote={We investigate Fr\"ohlich-like electron--optical-phonon interactions in wurtzite structures with single and double heterointerfaces based on the macroscopic dielectric continuum model and the uniaxial model. In addition to confined (for the case of double interfaces), interface, and half-space optical phonon modes as expected from the analogy with zinc-blende structures, propagating modes may exist in wurtzite heterosystems due to anisotropic phonon dispersion. This is especially the case when the dielectric properties of the adjacent heterostructure materials do not differ substantially. The dispersion relations and the interaction Hamiltonians for each of these modes are derived.}, number={8}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Lee, B. C. and Kim, K. W. and Stroscio, M. A. and Dutta, M.}, year={1998}, month={Aug}, pages={4860–4865} }
 @article{teng_sun_haddad_stroscio_yu_kim_1998, title={Phonon assisted intersubband transitions in step quantum well structures}, volume={84}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.368277}, DOI={10.1063/1.368277}, abstractNote={We evaluate effects of heterointerfaces on optical phonon modes and phonon assisted electron intersubband transition rates in step quantum well structures for intersubband lasers. Various phonon modes and electron–phonon interaction Hamiltonians, including the interface modes, confined longitudinal-optical modes, and half space modes in the quantum well structures are calculated based on the macroscopic dielectric continuum model and microscopic analysis. The transfer matrix method is used to calculate the interface modes. The intersubband transition rates due to electron–phonon scattering by these phonon modes are evaluated using Fermi’s golden rule, with the electron wave functions obtained by solving the Schrödinger equation for the heterostructures under investigation. Our results show that, compared with the transition rates in the same structures calculated using the bulk phonon modes and the bulk Fröhlich interaction Hamiltonian, the electron interface–phonon interactions give significantly larger transition rates up to an order of magnitude. Therefore, the effects of localized phonon modes, especially the interface modes, must be taken into consideration for optimal device design.}, number={4}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Teng, H. B. and Sun, J. P. and Haddad, G. I. and Stroscio, Michael A. and Yu, SeGi and Kim, K. W.}, year={1998}, month={Aug}, pages={2155–2164} }
 @article{komirenko_kim_stroscio_kochelap_1998, title={Renormalization of acoustic phonon spectra and rudiments of the Peierls transition in free-standing quantum wires}, volume={58}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.58.16360}, DOI={10.1103/physrevb.58.16360}, abstractNote={We have analyzed a quasi-one-dimensional electron-phonon system coupled through the deformation potential interaction. In a free-standing quantum wire, we calculated the renormalization of acoustic phonon spectra. The results illustrate remarkable cusplike features in the vicinity of the phonon wave vector that is twice the electron Fermi wave vector. These cusps are rudiments of the Peierls transition in the quasi-one-dimensional system. The transition is suppressed in conventional materials because of the electrostatic effects. For such materials, however, the renormalization of acoustic phonon spectra and the cusps can be observed in various acoustical and optical experiments. Furthermore, our study demonstrates that the Peierls transition can occur in free-standing quantum wires fabricated from semiconductor materials with high permittivity.}, number={24}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Komirenko, S. M. and Kim, K. W. and Stroscio, M. A. and Kochelap, V. A.}, year={1998}, month={Dec}, pages={16360–16368} }
 @article{williams_hulfachor_kim_littlejohn_holton_1998, title={Scaling trends for device performance and reliability in channel-engineered n-MOSFETs}, volume={45}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.658839}, DOI={10.1109/16.658839}, abstractNote={Channel-engineered MOSFETs with retrograde doping profiles are expected to provide increased carrier mobility and immunity to short channel effects. However, the physical mechanisms responsible for device performance of retrograde designs in the deep-submicron regime are not fully understood, and general device scaling trends are not well documented. Also, little effort has been devoted to the study of hot-electron-induced device degradation. In this paper, we employ a comprehensive simulation methodology to investigate scaling and device performance trends in channel-engineered n-MOSFETs. The method features an advanced ensemble Monte Carlo device simulator to extract hot-carrier reliability for super-steep-retrograde and more conventional silicon n-MOS designs with effective channel lengths scaled from 800 to 100 nm. With decreasing channel length, our simulations indicate that the retrograde design shows increasingly less total hot-electron injection into the oxide than the conventional design. However, near the 100-nm regime, the retrograde design provides less current drive, loses its advantage of higher carrier mobility, and exhibits much greater sensitivity to hot-electron-induced interface states when compared to the conventional device.}, number={1}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Williams, S.C. and Hulfachor, R.B. and Kim, K.W. and Littlejohn, M.A. and Holton, W.C.}, year={1998}, pages={254–260} }
 @article{wang_kim_littlejohn_1998, title={Self-consistent calculation of mode spectra and modulation response in wurtzite GaN quantum-well lasers}, volume={10}, ISSN={1041-1135 1941-0174}, url={http://dx.doi.org/10.1109/68.651100}, DOI={10.1109/68.651100}, abstractNote={The photon rate-equation formalism is used to evaluate the multimode photon density, the output lasing power, and the modulation frequency response in pseudomorphically strained wurtzite GaN quantum-well lasers. The formalism is based on a self-consistent methodology that couples an envelope function (or k/spl middot/p) Hamiltonian with Poisson's equation. From this approach, we consider (1) the band structure under the influence of large piezoelectric fields and with many-body effect; and (2) the stimulated and spontaneous emissions for each Fabry-Perot mode. Our calculations predict a threshold current density of approximately 1 kA/cm/sup 2/ and an intrinsic 3-dB modulation bandwidth of 11.7 GHz at 40-mW output power for a 50-/spl Aring/ pseudomorphically strained GaN-Al/sub 0.2/Ga/sub 0.8/N single-quantum-well (SQW) laser. Our estimation of the threshold current density represents the theoretical limit and is compatible with recent experimental results in InGaN multiple-quantum-well (MQW) lasers.}, number={1}, journal={IEEE Photonics Technology Letters}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wang, Jin and Kim, K.W. and Littlejohn, M.A.}, year={1998}, month={Jan}, pages={51–53} }
 @article{roze_bannov_kim_holton_littlejohn_1998, title={Temperature dependence of impact ionization coefficients in p-Si}, volume={83}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.367303}, DOI={10.1063/1.367303}, abstractNote={An efficient full-band Monte Carlo program for high-energy carrier transport is employed to investigate hole impact ionization in p-Si for a range of electric fields up to 800 kV/cm and lattice temperatures between 77 and 450 K. An empirical expression is developed for the temperature dependence of ionization coefficients. The results are compared with those obtained from existing models. The empirical model agrees well with experiments and other numerically intensive models, providing a means to incorporate these effects into other device simulators and reliability models.}, number={9}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Roze, K. and Bannov, N. A. and Kim, K. W. and Holton, W. C. and Littlejohn, M. A.}, year={1998}, month={May}, pages={4988–4990} }
 @article{lee_mansour_sirenko_kim_littlejohn_1997, title={Anisotropic hole scattering in hexagonal GaN}, volume={12}, ISSN={0268-1242 1361-6641}, url={http://dx.doi.org/10.1088/0268-1242/12/3/007}, DOI={10.1088/0268-1242/12/3/007}, abstractNote={We calculate the hole scattering rate owing to the interaction with polar optical phonons and ionized impurities in bulk wurtzite GaN. The valence band states of this hexagonal material are obtained from a matrix Hamiltonian. The calculated scattering rate shows strong orientational dependence with respect to the crystal c-axis. Analysis shows that both anisotropy in the dispersion relations and the Bloch overlap factors are important for a proper description of hole scattering.}, number={3}, journal={Semiconductor Science and Technology}, publisher={IOP Publishing}, author={Lee, B C and Mansour, N S and Sirenko, Yu M and Kim, K W and Littlejohn, M A}, year={1997}, month={Mar}, pages={280–283} }
 @article{wang_kim_littlejohn_1997, title={Carrier capture in pseudomorphically strained wurtzite GaN quantum-well lasers}, volume={71}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.119657}, DOI={10.1063/1.119657}, abstractNote={The generalized photon-carrier rate-equation formalism is used to evaluate the carrier capture process in pseudomorphically strained wurtzite GaN quantum-well lasers. Our results show that both the carrier capture time and the carrier escape time vary significantly with the injected carrier density and strain-induced piezoelectric field. Thus, it is demonstrated that in place of the flatband conditions adopted in most treatments, a self-consistent adjustment of the carrier capture process is essential for achieving an accurate description of carrier dynamics in wurtzite GaN quantum-well lasers.}, number={6}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Wang, Jin and Kim, K. W. and Littlejohn, M. A.}, year={1997}, month={Aug}, pages={820–822} }
 @article{hulfachor_kim_littlejohn_osburn_1997, title={Effects of silicon layer properties on device reliability for 0.1-μm SOI n-MOSFET design strategies}, volume={44}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.568044}, DOI={10.1109/16.568044}, abstractNote={We employ an advanced simulation method to investigate the effects of silicon layer properties on hot-electron-induced reliability for two 0.1-/spl mu/m SOI n-MOSFET design strategies. The simulation approach features a Monte Carlo device simulator in conjunction with commercially available process and device simulators. The two channel designs are: 1) a lightly-doped (10/sup 16/ cm/sup -3/) channel and 2) a heavily-doped (10/sup 18/ cm/sup -3/) channel. For each design, the silicon layer thicknesses (T/sub Si/) of 30, 60, and 90 nm are considered. The devices are biased under low-voltage conditions where the drain voltage is considerably less than the Si/SiO/sub 2/ barrier height for electron injection. A comparative analysis of the Monte Carlo simulation results shows that an increase in T/sub Si/ results in decreasing hot electron injection into the back oxide in both device designs. However, electron injection into the front oxide exhibits opposite trends of increasing injection for the heavily-doped channel design and decreasing injection for the lightly-doped channel design. These important trends are attributed to highly two-dimensional electric field and current density distributions. Simulations also show that the lightly-doped channel design is about three times more reliable for thick silicon layers. However, as the silicon layer is thinned to 30 nm, the heavily-doped channel design becomes about 10% more reliable instead.}, number={5}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Hulfachor, R.B. and Kim, K.W. and Littlejohn, M.A. and Osburn, C.M.}, year={1997}, month={May}, pages={815–821} }
 @article{lee_kim_dutta_stroscio_1997, title={Electron–optical-phonon scattering in wurtzite crystals}, volume={56}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.56.997}, DOI={10.1103/physrevb.56.997}, abstractNote={We present Fr\"ohlich-like electron--optical-phonon interaction Hamiltonian for wurtzite crystals in the long-wavelength limit based on the macroscopic dielectric continuum model and the uniaxial model. In general, the optical-phonon branches support mixed longitudinal and transverse modes due to the anisotropy. We calculate electron scattering rate due to the optical phonons in the bulk wurtzite GaN and demonstrate that the scattering rate due to transverselike phonon processes can be strongly enhanced over a range of angles with respect to the $c$ axis. For the case of longitudinal-like modes, the anisotropy is small and the result is almost the same as that obtained with the cubic Fr\"ohlich Hamiltonian.}, number={3}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Lee, B. C. and Kim, K. W. and Dutta, M. and Stroscio, M. A.}, year={1997}, month={Jul}, pages={997–1000} }
 @article{sirenko_jeon_lee_kim_littlejohn_stroscio_iafrate_1997, title={Hole scattering and optical transitions in wide-band-gap nitrides: Wurtzite and zinc-blende structures}, volume={55}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.55.4360}, DOI={10.1103/PhysRevB.55.4360}, abstractNote={The energy spectrum and transitions of valence-band carriers in wurtzite materials are studied theoretically using cubic crystals for comparison. We correct the commonly used cubic approximation and propose notations for Luttinger-like parameters in wurtzite structures that simplify the cubic approximation to ${\ensuremath{\gamma}}_{1\mathrm{z}}$=${\ensuremath{\gamma}}_{1\mathrm{\ensuremath{\perp}}}$, ${\ensuremath{\gamma}}_{2\mathrm{z}}$=${\ensuremath{\gamma}}_{2\mathrm{\ensuremath{\perp}}}$, and ${\ensuremath{\gamma}}_{3\mathrm{z}}$=${\ensuremath{\gamma}}_{3\mathrm{\ensuremath{\perp}}}$. We establish the relation between two recently proposed 3\ifmmode\times\else\texttimes\fi{}3 matrix blocks diagonalizing the full 6\ifmmode\times\else\texttimes\fi{}6 Hamiltonian and provide geometric interpretation in three-dimensional Bloch space. The formalism is used then to derive transition matrix elements for three types of processes: (i) macrofield hole scattering, described by the Bloch overlap factor; (ii) optical transitions between conduction and valence bands; and (iii) intervalence band optical transitions. Finally, we discuss the set of material parameters for group-III nitrides and present the numerical results.}, number={7}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Sirenko, Yu. M. and Jeon, J. B. and Lee, B. C. and Kim, K. W. and Littlejohn, M. A. and Stroscio, M. A. and Iafrate, G. J.}, year={1997}, month={Feb}, pages={4360–4375} }
 @article{sirenko_kim_stroscio_1997, title={Near-surface electrons and acoustic phonons: Energy and momentum relaxation}, volume={56}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.56.15770}, DOI={10.1103/physrevb.56.15770}, abstractNote={We study energy and momentum relaxation of a two-dimensional (2D) electron channel located at a finite distance $\mathcal{l}$ from a free crystal surface. The interaction with a complete set of bulklike, totally reflected, and Rayleigh acoustic phonon modes is taken into account. In most cases of interest the relaxation rates have the same temperature dependence as for 2D or bulk electrons interacting with bulk phonons. Numerical calculations demonstrate that the presence of a surface results in approximately a 10% modification of scattering rates in the high-temperature region. In the opposite limit (Bloch-Gr\"uneisen regime), the contribution of the surface phonons may dominate over that of bulklike modes. Oscillations of the relaxation rates as a function of the distance $\mathcal{l}$ between the electron channel and the surface are also predicted.}, number={24}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Sirenko, Yuri M. and Kim, K. W. and Stroscio, Michael A.}, year={1997}, month={Dec}, pages={15770–15781} }
 @article{wang_jeon_sirenko_kim_1997, title={Piezoelectric effect on optical properties of pseudomorphically strained wurtzite GaN quantum wells}, volume={9}, ISSN={1041-1135 1941-0174}, url={http://dx.doi.org/10.1109/68.584971}, DOI={10.1109/68.584971}, abstractNote={The presence of internal strain in wurtzite quantum-well (QW) structures may lead to the generation of large polarization fields. These piezoelectric fields cause a spatial separation of the electrons and holes inside the QW to screen the internal fields. A self-consistent calculation of optical gain and the corresponding differential gain is presented in pseudomorphically strained GaN quantum wells as a function of carrier density. Based on the local exchange-correlation potential, electron and hole band structures are obtained by coupling Poisson's equation with an effective-mass Schrodinger equation in the conduction band and an envelope-function (or k/spl middot/p) Hamiltonian in the valence band. Our calculations show that self-consistent calculations including the piezoelectric effects are essential for accurate description of strained wurtzite QW structures.}, number={6}, journal={IEEE Photonics Technology Letters}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wang, Jin and Jeon, J.B. and Sirenko, Yu.M. and Kim, K.W.}, year={1997}, month={Jun}, pages={728–730} }
 @inproceedings{wang_jeon_kim_littlejohn_1997, title={Self-consistent study of strained wurtzite GaN quantum-well lasers}, ISBN={0780339703}, url={http://dx.doi.org/10.1109/cornel.1997.649371}, DOI={10.1109/cornel.1997.649371}, abstractNote={The photon rate-equation formalism is used to evaluate the multi-mode photon density, the output lasing power, and the modulation frequency response in pseudomorphically-strained wurtzite GaN quantum-well lasers. The formalism is based on a self-consistent methodology that couples an envelope-function (or k/spl middot/p) Hamiltonian with Poisson's equation. From this approach, we consider (a) the band structure under the influence of large piezoelectric fields and with many-body effect; and (b) the stimulated and spontaneous emissions for each Fabry-Perot mode. Also the influence of carrier capture processes on the band structure and modulation response is studied by the generalized rate-equation.}, booktitle={Proceedings IEEE/Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits CORNEL-97}, publisher={IEEE}, author={Wang, J. and Jeon, J.B. and Kim, K.W. and Littlejohn, M.A.}, year={1997}, pages={306–313} }
 @article{jeon_lee_sirenko_kim_littlejohn_1997, title={Strain effects on optical gain in wurtzite GaN}, volume={82}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.365824}, DOI={10.1063/1.365824}, abstractNote={Strain effects on optical gain in hexagonal bulk GaN are calculated and explained in terms of the change in the effective hexagonal crystal field component. Qualitatively, even unstrained wurtzite structures correspond to cubic crystals with a proper biaxial stress applied. Such biaxial stress results in effective tensile deformation along the c axis ([111] direction in cubic crystals) and compressive strain in the perpendicular plane. Therefore, the light mode with a polarization vector parallel to the c axis is suppressed, while the mode with a perpendicular polarization is enhanced in wurtzite structures. Thus, compared to cubic structures with similar material parameters, a strong optical anisotropy of wurtzites results in enhanced gain for certain light polarizations, which make wurtzite structures superior for lower-threshold lasing. These qualitative arguments are illustrated by numerical calculations of optical gain in biaxially strained wurtzite GaN, based on a 6×6 envelope-function Hamiltonian.}, number={1}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Jeon, J. B. and Lee, B. C. and Sirenko, Yu. M. and Kim, K. W. and Littlejohn, M. A.}, year={1997}, month={Jul}, pages={386–391} }
 @article{yu_kim_stroscio_iafrate_sun_haddad_1997, title={Transfer matrix method for interface optical-phonon modes in multiple-interface heterostructure systems}, volume={82}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.365649}, DOI={10.1063/1.365649}, abstractNote={Interactions of carriers with interface optical phonons dominate over other carrier–phonon scatterings in narrow quantum-well structures. Herein, a transfer matrix method is used to establish a formalism for determining the dispersion relations, electrostatic potentials, and Fröhlich interaction Hamiltonians of the interface optical phonons for multiple-interface heterostructure systems within the framework of the macroscopic dielectric continuum model. This method facilitates systematic calculations for complex structures where the conventional method is very difficult to implement. Several specific cases are treated to illustrate the advantages of the general formalism.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Yu, SeGi and Kim, K. W. and Stroscio, Michael A. and Iafrate, G. J. and Sun, J.-P. and Haddad, G. I.}, year={1997}, month={Oct}, pages={3363–3367} }
 @article{mansour_kim_bannov_littlejohn_1997, title={Transient ballistic transport in GaN}, volume={81}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.363952}, DOI={10.1063/1.363952}, abstractNote={Monte Carlo simulations have been used to study the spatial scales of electron ballistic transport in GaN. The large optical phonon energy (92 meV) and the large intervalley energy separation between the Γ and satellite conduction band valleys (⩾1.5 eV) suggest an increasing role for ballistic electron effects in GaN, especially when compared with most III–V semiconductors such as GaAs. However, the concomitant high polar optical phonon scattering rate in GaN tends to diminish the desirable electron transport properties. The relationships between these two factors have been studied for the range of electric fields up to 140 kV/cm and lattice temperatures between 300 and 600 K. We demonstrate that in most cases electrons in GaN lose their directed average velocity over distances of only 100−200 Å, and ballistic transport occurs only over such short distances. The main cause for the small spatial scales of ballistic transport in GaN is the strong electron–optical phonon coupling which results in rapid relaxation of the directed electron velocity.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Mansour, N. and Kim, K. W. and Bannov, N. A. and Littlejohn, M. A.}, year={1997}, month={Mar}, pages={2901–2903} }
 @article{sirenko_jeon_lee_kim_littlejohn_stroscio_1997, title={Valence band spectra in pseudomorphically strained wurtzite quantum wells}, volume={22}, ISSN={0749-6036}, url={http://dx.doi.org/10.1006/spmi.1996.0215}, DOI={10.1006/spmi.1996.0215}, abstractNote={Abstract A theory for the effects of size quantization and strain on the hole energy spectra in wurtzite AlGaN/GaN/AlGaN quantum wells is presented. The subband structure and dispersion relations for holes in pseudomorphically strained rectangular wells are obtained using an analytical solution of Schrodinger's equation with 3 × 3 matrix Hamiltonian blocks. The effects of strain are interpreted using an analogy between wurzite structures and prestrained zincblende crystals.}, number={2}, journal={Superlattices and Microstructures}, publisher={Elsevier BV}, author={Sirenko, Yu.M. and Jeon, J.-B. and Lee, B.C. and Kim, K.W. and Littlejohn, M.A. and Stroscio, M.A.}, year={1997}, month={Sep}, pages={195–198} }
 @article{stroscio_sirenko_yu_kim_1996, title={Acoustic phonon quantization in buried waveguides and resonators}, volume={8}, ISSN={0953-8984 1361-648X}, url={http://dx.doi.org/10.1088/0953-8984/8/13/006}, DOI={10.1088/0953-8984/8/13/006}, abstractNote={Starting from a classical Hamiltonian for nonhomogeneous elastic media, a procedure is developed for acoustic phonon quantization in resonators as well as linear and planar waveguides. The formalism is illustrated in an example of acoustic phonon modes in a buried cylindrical waveguide. The deformation potential Hamiltonian for electron - acoustic phonon interaction is also obtained.}, number={13}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Stroscio, M A and Sirenko, Yu M and Yu, S and Kim, K W}, year={1996}, month={Mar}, pages={2143–2151} }
 @article{mansour_sirenko_kim_littlejohn_stroscio_1996, title={Carrier capture in quantum well embedded quantum wire structures}, volume={69}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.118060}, DOI={10.1063/1.118060}, abstractNote={We propose a novel quantum wire (QWR) laser structure with improved carrier capture characteristics, where the carriers are injected into a quantum well (QWL) and subsequently recombine within an embedded QWR. The corresponding electron capture rates via polar optical phonon scattering are calculated for this system. An oscillatory behavior of the electron capture rate is observed as a function of the QWR thickness at the temperatures considered (77 K and 300 K). The amplitude of these oscillations also increases as the QWR width decreases. Our calculations show that the electron capture rate in the QWL embedded QWR structure can be improved by more than 30% when compared to single QWLs. Therefore, the proposed QWR laser design provides improved modulation bandwidth and optical gain over conventional QWL and QWR structures.}, number={3}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Mansour, N. S. and Sirenko, Yu. M. and Kim, K. W. and Littlejohn, M. A. and Stroscio, M. A.}, year={1996}, month={Jul}, pages={360–362} }
 @article{hulfachor_kim_littlejohn_osburn_1996, title={Comparative analysis of hot electron injection and induced device degradation in scaled 0.1 μm SOI n-MOSFETs using Monte Carlo simulation}, volume={17}, ISSN={0741-3106 1558-0563}, url={http://dx.doi.org/10.1109/55.484121}, DOI={10.1109/55.484121}, abstractNote={A self-consistent Monte Carlo (MC) simulator is employed to investigate and compare hot electron phenomena in three competing design strategies for 0.1 /spl mu/m SOI n-MOSFETs operating under low voltage conditions, i.e., V/sub d/ considerably less than the Si-SiO/sub 2/ injection barrier height /spl phi//sub b/. Simulations of these designs reveal that non-local carrier transport effects and two-dimensional current how play a significant role in determining the relative rate and location of hot electron injection into both the front and back oxides. Specifically, simulations indicate that electron-electron interactions near the drain edge are a main source of electron energies exceeding /spl phi//sub b/. The hot electron injection distributions are then coupled with an empirical model to generate interface state distributions at both the front and back oxide interfaces. These interface states are incorporated into a drift-diffusion simulator to examine relative hot-electron-induced device degradation for the three 0.1 /spl mu/m SOI designs. Simulations suggest that both the Si layer thickness and doping distribution affect device sensitivity to hot-electron-induced interface states. In particular, the simulations show that a decrease in the channel doping results in increased sensitivity to back oxide charge. In the comparison of the heavily-doped designs, the design with a thinner T/sub Si/ experiences significantly more hot-electron-induced oxide damage in the back oxide and more degradation from the charged states at the back interface.}, number={2}, journal={IEEE Electron Device Letters}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Hulfachor, R.B. and Kim, K.W. and Littlejohn, M.A. and Osburn, C.M.}, year={1996}, month={Feb}, pages={53–55} }
 @article{sirenko_stroscio_kim_1996, title={Dynamics of cytoskeletal filaments}, volume={54}, ISSN={1063-651X 1095-3787}, url={http://dx.doi.org/10.1103/PhysRevE.54.1816}, DOI={10.1103/PhysRevE.54.1816}, abstractNote={We apply elasticity theory formalism to study long-range, collective vibrations of actin and intermediate filaments, which are long cylindrical macromolecules and constitute part of the cytoskeleton network in eukariotic cells. The dispersion relations are obtained for elastic waves propagating in the vicinity of filaments which are modeled as elastic cylindrical rods immersed in a liquid. In the long-wavelength limit the filament-water system supports two acoustic modes with propagation speeds of approximately 800 and 1300 m/s and a single flexural wave with parabolic dispersion law. The presence of solvent leads to radiation of acoustic energy from waves with a phase velocity exceeding the speed of sound of water. Our study complements the existing normal-mode analysis of free actin filament vibrations and generalizes these results for different structures as well as including the effects of solvents. \textcopyright{} 1996 The American Physical Society.}, number={2}, journal={Physical Review E}, publisher={American Physical Society (APS)}, author={Sirenko, Yuri M. and Stroscio, Michael A. and Kim, K. W.}, year={1996}, month={Aug}, pages={1816–1823} }
 @article{sirenko_stroscio_kim_1996, title={Elastic vibrations of microtubules in a fluid}, volume={53}, ISSN={1063-651X 1095-3787}, url={http://dx.doi.org/10.1103/PhysRevE.53.1003}, DOI={10.1103/PhysRevE.53.1003}, abstractNote={We study thoreticaly vibrational properties of microtubules (MTs), which are long hollow cylindrical macromolecules with a diameter of the order of 25 nm and serve as a major component of cytoskeleton in eukariotic cells. Modeling MTs by thin elastic cylindrical shells, we derive the eigenfrequencies and eigenmodes of confined elastic vibrations in a shell-fluid system. Numerical calculations, based on recently obtained experimental data for Young's modulus of MT, show that MT-water system supports interface elastic waves with maximal frequencies in a gigahertz range. In a long-wavelength limit, there exist three axisymmetric acoustic waves with velocities of about 200 to 600 m/s, and an infinite set of helical waves with a parabolic dispersion law. \textcopyright{} 1996 The American Physical Society.}, number={1}, journal={Physical Review E}, publisher={American Physical Society (APS)}, author={Sirenko, Yuri M. and Stroscio, Michael A. and Kim, K. W.}, year={1996}, month={Jan}, pages={1003–1010} }
 @inbook{erdogan_sankaran_kim_stroscio_iafrate_1996, series={Institute of Physics Series}, title={Electric field induced type-I to type-II switching in GaAs/AlAs quantum wells}, volume={145}, booktitle={Proceedings of the 22nd International Symposium on Compound Semiconductors}, author={Erdogan, M.U. and Sankaran, V. and Kim, K.W. and Stroscio, M.A. and Iafrate, G.J.}, year={1996}, pages={1199–1202}, collection={Institute of Physics Series} }
 @article{yu_kim_stroscio_iafrate_ballato_1996, title={Electron interaction with confined acoustic phonons in cylindrical quantum wires via deformation potential}, volume={80}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.363199}, DOI={10.1063/1.363199}, abstractNote={The effects of phonon confinement on electron–acoustic-phonon scattering is studied in cylindrical semiconductor quantum wires. In the macroscopic elastic continuum model, the confined-phonon dispersion relations are obtained for several crystallographic directions with the two cardinal boundary conditions: free-surface and clamped-surface boundary conditions. The scattering rates due to the deformation potential interaction are obtained for these confined phonons and are compared with those of bulk-like phonons for a number of quantum wire materials. The results show that the inclusion of acoustic phonon confinement effects may be crucial for calculating accurate low-energy electron scattering rates in nanostructures. It is also demonstrated that the scattering rates may be significantly influenced by the direction of phonon propagation, especially for low-energy electrons. Furthermore, it has been found that there is a scaling rule governing the directional dependence of the scattering rates: the directions characterized by small Poisson ratios exhibit large scattering rates.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Yu, SeGi and Kim, K. W. and Stroscio, Michael A. and Iafrate, G. J. and Ballato, Arthur}, year={1996}, month={Sep}, pages={2815–2822} }
 @article{ellis-monaghan_hulfachor_kim_littlejohn_1996, title={Ensemble Monte Carlo study of interface-state generation in low-voltage scaled silicon MOS devices}, volume={43}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.502424}, DOI={10.1109/16.502424}, abstractNote={An ensemble Monte Carlo (MC) model coupled with an interface-state generation model was employed to predict the quantity and lateral distribution of hot-electron-induced interface states in scaled silicon MOSFETs. Constant field and more generalized scaling methods were used as the basis to simulate devices with 0.33-, 0.20-, and 0.12-/spl mu/m channel lengths. The dependencies of interface-state generation on applied bias and electric field profiles were investigated. Hot-electron injection and interface-state density profiles were simulated at biases as low as 1.44 V (i.e., lower than the 3.1 V potential barrier at the Si/SiO/sub 2/ interface). These simulations demonstrate that "lucky electron" and/or electron temperature models are no longer accurate for predicting hot-electron effects in such regimes. Electron-electron scattering is shown to be a critical consideration for simulation of hot-electron injection at low drain to source bias voltages, where local interfacial barrier heights are greater than the energy gained by an electron from the applied electric field. Simulations indicate that a scaled decrease in the channel length of a device may be accompanied by an increase in the lateral electric field without incurring a penalty for higher hot-electron degradation. It is also shown that conventional hot-electron stressing using accelerated stress bias conditions may continue to be valuable for predicting the reliability of device designs scaled to 0.1-/spl mu/m channel lengths.}, number={7}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Ellis-Monaghan, J.J. and Hulfachor, R.B. and Kim, K.W. and Littlejohn, M.A.}, year={1996}, month={Jul}, pages={1123–1132} }
 @article{sirenko_jeon_kim_littlejohn_stroscio_1996, title={Envelope-function formalism for valence bands in wurtzite quantum wells}, volume={53}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.53.1997}, DOI={10.1103/PhysRevB.53.1997}, abstractNote={A theoretical treatment of the valence-band spectrum of wurtzite-type materials is developed starting from the Rashba-Sheka-Pikus (RSP) 6\ifmmode\times\else\texttimes\fi{}6 matrix Hamiltonian for coupled ${\mathrm{\ensuremath{\Gamma}}}_{9}$, ${\mathrm{\ensuremath{\Gamma}}}_{7}$, and ${\mathrm{\ensuremath{\Gamma}}}_{7}$ levels. A unitary transformation is applied in order to diagonalize the RSP Hamiltonian to two 3\ifmmode\times\else\texttimes\fi{}3 blocks and the results are compared with those obtained for cubic structures [C. Y.-P. Chao and S. L. Chuang, Phys. Rev. B 46, 4110 (1992)]. Using the diagonalized form of the Hamiltonian, a solution for hole states in wurtzite quantum wells (QW's) is constructed and explicit expressions for the QW valence subband edges are obtained. We suggest that parameters of the RSP Hamiltonian for w\"urtzite structures can be deduced from experimental observations of the energy separation between edges of the hole subbands in QW's. \textcopyright{} 1996 The American Physical Society.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Sirenko, Yu. M. and Jeon, J.-B. and Kim, K. W. and Littlejohn, M. A. and Stroscio, M. A.}, year={1996}, month={Jan}, pages={1997–2009} }
 @article{erdoğan_sankaran_kim_stroscio_iafrate_1996, title={Optical properties of ultrathin GaAs/AlAs quantum well structures with an electric field}, volume={79}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.362493}, DOI={10.1063/1.362493}, abstractNote={A theoretical study of the optical properties of GaAs/AlAs quantum well structures in the presence of an electric field is presented. In the first part of the article, interband transitions from the valence band to the conduction band are studied near the type-I to type-II transition point. In the second part, the effect of the electric field on intersubband transitions within the conduction band is considered. The band structure is calculated using a second-nearest-neighbor empirical sp3 tight binding method including spin–orbit effects. Interband and intersubband transition energies, optical matrix elements, and absorption coefficients are given as functions of the electric field. It is shown that the optical properties of these structures can be modified significantly with field near the anticrossing point.}, number={11}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Erdoğan, M. U. and Sankaran, V. and Kim, K. W. and Stroscio, M. A. and Iafrate, G. J.}, year={1996}, month={Jun}, pages={8675–8681} }
 @article{hulfachor_ellis-monaghan_kim_littlejohn_1996, title={Spatial retardation of carrier heating in scaled 0.1-μm n-MOSFET's using Monte Carlo simulations}, volume={43}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.485550}, DOI={10.1109/16.485550}, abstractNote={A comprehensive Monte Carlo simulator is employed to investigate nonlocal carrier transport in 0.1 /spl mu/m n-MOSFET's under low-voltage stress. Specifically, the role of electron-electron (e-e) interactions on hot electron injection is explored for two emerging device designs biased at a drain voltage V/sub d/ considerably less than the Si/SiO/sub 2/ injection barrier height /spl phi//sub b/. Simulation of both devices reveal that 1) although qV/sub d/</spl phi//sub b/, carriers can obtain energies greater than /spl phi//sub b/, and 2) the peak for electron injection is displaced approximately 20 nm beyond the peak in the parallel channel electric field. These phenomena constitute a spatial retardation of carrier heating that is strongly influenced by e-e interactions near the drain edge. (Virtually no injection is observed in our simulations when e-e scattering is not considered.) Simulations also show that an aggressive design based on larger dopant atoms, steeper doping gradients, and a self-aligned junction counter-doping process produces a higher peak in the channel electric field, a hotter carrier energy distribution, and a greater total electron injection rate into the oxide when compared to a more conventionally-doped design. The impact of spatially retarded carrier heating on hot-electron-induced device degradation is further examined by coupling an interface state distribution obtained from Monte Carlo simulations with a drift-diffusion simulator. Because of retarded carrier heating, the interface states are mainly generated further over the drain region where interface charge produces minimal degradation. Thus, surprisingly, both 0.1 /spl mu/m n-MOSFET designs exhibit comparable drain current degradation rates.}, number={4}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Hulfachor, R.B. and Ellis-Monaghan, J.J. and Kim, K.W. and Littlejohn, M.A.}, year={1996}, month={Apr}, pages={661–663} }
 @article{sirenko_jeon_kim_littlejohn_stroscio_1996, title={Strain effects on valence band structure in würtzite GaN quantum wells}, volume={69}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.117721}, DOI={10.1063/1.117721}, abstractNote={The effect of strain on valence band spectra in both bulk and in pseudomorphic GaN quantum wells is studied theoretically using recent experimental results for deformation potential constants. Wave functions and dispersion curves for A-, B- and C-hole subbands are obtained from linear combination of bulk analytical solutions for the 3×3 würtzite block-Hamiltonian. A detailed analysis is presented for the dependence of hole spectrum on quantum well width, depth, and strain due to lattice mismatch.}, number={17}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Sirenko, Yu. M. and Jeon, J.‐B. and Kim, K. W. and Littlejohn, M. A. and Stroscio, M. A.}, year={1996}, month={Oct}, pages={2504–2506} }
 @article{sankaran_kim_iafrate_1996, title={Tight-binding study of optical properties in short-periodIn0.53Ga0.47As/InP superlattices}, volume={53}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.53.6939}, DOI={10.1103/PhysRevB.53.6939}, abstractNote={We present theoretical calculations of the imaginary part of the dielectric function, ${\mathrm{\ensuremath{\varepsilon}}}_{2}$(\ensuremath{\omega}), of ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As/InP superlattices (SL's). An empirical tight-binding (TB) description of electronic states, including spin-orbit effects, is employed. We demonstrate that the absorption spectra of the constituent bulk materials can be reproduced very well with an appropriate choice of values for optical matrix elements between TB basis functions. These parameters then yield the absorption spectra of SL's. We have calculated ${\mathrm{\ensuremath{\varepsilon}}}_{2}$(\ensuremath{\omega}) for ultrathin (${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As${)}_{\mathit{n}}$/(InP${)}_{\mathit{n}}$ SL's with n=2 and 4. The computed ${\mathrm{\ensuremath{\varepsilon}}}_{2}$ of SL's shows features similar to those found in the spectra of bulk constituents with some discernible effects due to confinement and SL periodicity. \textcopyright{} 1996 The American Physical Society.}, number={11}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Sankaran, V. and Kim, K. W. and Iafrate, G. J.}, year={1996}, month={Mar}, pages={6939–6942} }
 @article{jeon_sirenko_kim_littlejohn_stroscio_1996, title={Valence band parameters of wurtzite materials}, volume={99}, ISSN={0038-1098}, url={http://dx.doi.org/10.1016/0038-1098(96)00282-7}, DOI={10.1016/0038-1098(96)00282-7}, abstractNote={We deduced the valence band parameters of several würtzite materials (ZnS, CdS, CdSe, and GaN) by matching the results of existing full-band calculations of the energy spectrum with analytical expressions of the envelope-function formalism. The calculated A-, B-, and C-type hole dispersion relations show strongly anisotropic characteristics and anti-crossing features in spectrum due to band mixing effects. We demonstrated that for all materials considered except CdSe, the spherical cubic approximation for six Luttinger-like parameters holds with good accuracy, so that the anisotropy arises mainly owing to the crystal field splitting term. Thus, the top valence band may be described with (in addition to crystal field and spin-orbit splitting energies) only two Luttinger-like parameters, γ1 and γ2.}, number={6}, journal={Solid State Communications}, publisher={Elsevier BV}, author={Jeon, J.-B. and Sirenko, Yu.M. and Kim, K.W. and Littlejohn, M.A. and Stroscio, M.A.}, year={1996}, month={Aug}, pages={423–426} }
 @article{sirenko_stroscio_kim_mitin_1995, title={Ballistic propagation of interface optical phonons}, volume={51}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.51.9863}, DOI={10.1103/PhysRevB.51.9863}, abstractNote={We discuss a spatial propagation of interface optical phonons in semiconductor heterostructures. Starting from a quantum kinetic equation for the nondiagonal phonon density operator, we derive the wave-packet presentation for the phonon amplitude for the pure initial phonon state. For small wave vectors, the group velocity determining the speed of the packet can exceed substantially the speed of sound and the wave front can propagate a distance of several micrometers before decay of the optical phonons. The possibility of experimental observation of the effect is discussed.}, number={15}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Sirenko, Yuri M. and Stroscio, Michael A. and Kim, K. W. and Mitin, Vladimir}, year={1995}, month={Apr}, pages={9863–9866} }
 @article{mansour_sirenko_kim_littlejohn_wang_leburton_1995, title={Carrier capture in cylindrical quantum wires}, volume={67}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.115253}, DOI={10.1063/1.115253}, abstractNote={We present quantum mechanical calculations of electron capture rates in cylindrical quantum wires via polar-optical phonon scattering. The capture rate dependence on quantum wire radius and lattice temperature is investigated. An oscillatory behavior of the electron capture rate is observed as a function of the quantum wire radius at the temperatures considered in this study (20–300 K). However, the amplitude of these oscillations decreases significantly at large wire radii and high lattice temperatures.}, number={23}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Mansour, N. S. and Sirenko, Yu. M. and Kim, K. W. and Littlejohn, M. A. and Wang, J. and Leburton, J. P.}, year={1995}, month={Dec}, pages={3480–3482} }
 @article{erdoǧan_kim_stroscio_1995, title={Effect of strain on hole tunneling dynamics in double barrier heterostructures}, volume={17}, ISSN={0749-6036}, url={http://dx.doi.org/10.1006/spmi.1995.1047}, DOI={10.1006/spmi.1995.1047}, abstractNote={Abstract A study of the effects of strain due to external stress and lattice mismatch on hole tunneling times in double barrier heterostructures is presented. The band structure of holes is calculated based on a k·p method within the envelope function approximation, including band mixing effects. The phase delay time is obtained from the energy derivative of the total phase shift of the wave function upon tunneling and is used to estimate the hole tunneling time. The results demonstrate that strain can be utilized to tailor hole tunneling times by changing the energy separation and, consequently, the mixing between heavy hole and light hole states in the quantum well.}, number={3}, journal={Superlattices and Microstructures}, publisher={Elsevier BV}, author={ErdoǦan, M.U. and Kim, K.W. and Stroscio, M.A.}, year={1995}, month={Apr}, pages={261} }
 @article{tian_kim_hauser_masnari_littlejohn_1995, title={Effects of profile doped elevated source/drain structures on deep-submicron MOSFETs}, volume={38}, ISSN={0038-1101}, url={http://dx.doi.org/10.1016/0038-1101(94)00160-H}, DOI={10.1016/0038-1101(94)00160-H}, abstractNote={Computer simulations have been carried out to systematically evaluate and compare device characteristics for various profile doped elevated source/drain (ESD) 0.25 μm channel-length MOSFET structures. In particular, characteristics for MOSFETs with a gradual profile doped ESD and for MOSFETs with an abrupt profile N+-N− doped ESD are examined in detail. Design considerations for key parameters related to the ESD formation (such as sidewall oxide width, elevation height and source/drain doping profile) and their influences on device characteristics are discussed. The results show the importance of ESD design parameters and structural optimization. They also indicate that the proposed gradual profile doped ESD MOSFETs can be as effective as the abrupt profile N+-N− doped ESD MOSFETs in achieving overall performance enhancement and reliability for deep-submicron device applications.}, number={3}, journal={Solid-State Electronics}, publisher={Elsevier BV}, author={Tian, H. and Kim, K.W. and Hauser, J.R. and Masnari, N.A. and Littlejohn, M.A.}, year={1995}, month={Mar}, pages={573–579} }
 @article{yu_kim_stroscio_iafrate_1995, title={Electron–acoustic-phonon scattering rates in cylindrical quantum wires}, volume={51}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.51.4695}, DOI={10.1103/PhysRevB.51.4695}, abstractNote={The electron--acoustic-phonon scattering rates in a cylindrical quantum wire are studied. Considering the quantum wire as an elastic continuum, the confined-phonon dispersion relation is calculated for two cardinal boundary conditions: free-surface and clamped-surface boundary conditions. The scattering rates due to the deformation-potential interaction are obtained for these two confined phonons and are compared with those of bulklike phonons. The results show that the inclusion of acoustic-phonon confinement effects may be crucial for calculating accurate low-energy-electron scattering rates in nanostructures. It is also demonstrated that the anisotropy should not be ignored for materials of cubic symmetry.}, number={7}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Yu, SeGi and Kim, K. W. and Stroscio, Michael A. and Iafrate, G. J.}, year={1995}, month={Feb}, pages={4695–4698} }
 @article{hulfachor_kim_littlejohn_osburn_1995, title={Non-local transport and 2-D effects on hot electron injection in fully-depleted 0.1 μm SOI n-MOSFET's using Monte Carlo simulation}, volume={28}, ISSN={0167-9317}, url={http://dx.doi.org/10.1016/0167-9317(95)00061-C}, DOI={10.1016/0167-9317(95)00061-C}, number={1-4}, journal={Microelectronic Engineering}, publisher={Elsevier BV}, author={Hulfachor, R.B. and Kim, K.W. and Littlejohn, M.A. and Osburn, C.M.}, year={1995}, month={Jun}, pages={289–292} }
 @article{mansour_kim_littlejohn_1995, title={Theoretical study of electron transport in gallium nitride}, volume={77}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.358696}, DOI={10.1063/1.358696}, abstractNote={This paper describes characteristic electron transport properties for GaN in bulk and quantum well structures. First, ensemble Monte Carlo calculations of steady-state electron drift velocity in bulk GaN are presented as a function of applied electric field for different lattice temperatures. At 300 K, the calculated peak steady-state drift velocity is 2.8×107 cm/s and the threshold field is 160 kV/cm. It is found that the peak steady-state electron drift velocity decreases only slightly by about 20% as the temperature increases from 300 to 600 K while the threshold field increases slightly by about 20%. Therefore, in addition to its high temperature stability, GaN has a low temperature coefficient making it ideal for high temperature applications. For electron transport in heterostructures, quantum mechanical calculations of the electron capture rate in GaN-based quantum wells as a function of well thickness are also presented. An oscillatory behavior of the electron capture rate as a function of quantum well thickness is observed. It is found that the electron capture time oscillates between 2 and 30 ps, which is about an order of magnitude greater than capture times in GaAs quantum wells. The amplitude of oscillations decreased as the well thickness increased. These results suggest that electron transport and carrier collection in GaN are efficient processes for improved electronic and optoelectronic devices.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Mansour, N. S. and Kim, K. W. and Littlejohn, M. A.}, year={1995}, month={Mar}, pages={2834–2836} }
 @inbook{sankaran_kim_iafrate_1995, title={Tight-Binding calculation of linear optical-properties of IN0.53GA0.47AS alloys and heterostructures}, volume={141}, booktitle={Proceedings of the 21st International Symposium on Compound Semiconductors}, author={Sankaran, V. and Kim, K.W and Iafrate, G.J.}, year={1995}, pages={769–774} }
 @article{ellis‐monaghan_kim_littlejohn_1994, title={A Monte Carlo study of hot electron injection and interface state generation model for silicon metal‐oxide‐semiconductor field‐effect transistors}, volume={75}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.355752}, DOI={10.1063/1.355752}, abstractNote={This paper describes a model which can predict the quantity and lateral distribution of hot-electron-induced interface states in Si metal-oxide-semiconductor field-effect transistors (MOSFETs). The results are obtained using an advanced Monte Carlo method, which incorporates two lowest conduction energy bands from pseudopotential calculations, coupled with an interface state generation model. The coupled model simulates transport-induced hot electron emission from Si into SiO2 and the subsequent generation of interface states in MOSFETs operating under realistic high-voltage stress conditions. The calculations explore the sensitivity of the channel electron energy distribution to various Monte Carlo parameters, such as impact ionization coefficients, self-consistent electron-electron interactions, and surface scattering. Within the validity of our treatments of these physical phenomena, it is shown that while the effects of Monte Carlo parameters on the energy distribution can result in uncertainties in the net interface state generation, quantitative studies may be allowed by using scaling principles. The interface state distribution obtained from the model agrees with experimental data from charge pumping measurements. The model also predicts that the interface state generation extends spatially beyond the range which is accessible by the charge pumping measurements.}, number={10}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Ellis‐Monaghan, John J. and Kim, K. W. and Littlejohn, Michael A.}, year={1994}, month={May}, pages={5087–5094} }
 @inproceedings{kim_yu_erdogan_stroscio_iafrate_1994, title={Acoustic phonons in rectangular quantum wires: approximate compressional modes and the corresponding deformation potential interactions}, url={http://dx.doi.org/10.1117/12.175912}, DOI={10.1117/12.175912}, abstractNote={The Hamiltonian describing the deformation potential interaction of confined acoustic phonons with carriers is derived by quantizing the appropriate, experimentally verified approximate compressional acoustic phonon modes in a rectangular quantum wire. The scattering rate due to the deformation potential interaction is calculated for a range of quantum wire dimensions.}, booktitle={Ultrafast Phenomena in Semiconductors}, publisher={SPIE}, author={Kim, Ki Wook and Yu, Segi and Erdogan, M. U. and Stroscio, Michael A. and Iafrate, Gerald J.}, editor={Ferry, David K. and van Driel, Henry M.Editors}, year={1994}, month={May} }
 @article{tian_hulfachor_ellis-monaghan_kim_littlejohn_hauser_masnari_1994, title={An evaluation of super-steep-retrograde channel doping for deep-submicron MOSFET applications}, volume={41}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.324605}, DOI={10.1109/16.324605}, abstractNote={Performance and reliability of deep-submicron MOSFET's employing super-steep-retrograde (SSR) channel doping configurations are examined using self-consistent Monte Carlo and drift-diffusion simulations. It is found that SSR channel doped MOSFET's provide increased current drive and reduced threshold voltage shift when compared with conventional MOSFET structures. However, they also display a relatively higher substrate current and interface state generation rate. The physical mechanisms of performance enhancement/degradation and design tradeoffs for SSR channel doped MOSFET's are discussed. >}, number={10}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Tian, H. and Hulfachor, R.B. and Ellis-Monaghan, J.J. and Kim, K.W. and Littlejohn, M.A. and Hauser, J.R. and Masnari, N.A.}, year={1994}, pages={1880–1882} }
 @article{tian_kim_littlejohn_woolard_1994, title={Application of near-ballistic transport in ultra-high-speed devices based on the potentials and limitations of a heterojunction launcher}, volume={9}, ISSN={0268-1242 1361-6641}, url={http://dx.doi.org/10.1088/0268-1242/9/5S/115}, DOI={10.1088/0268-1242/9/5S/115}, abstractNote={This paper presents a study of electron transport in ultra-high-speed devices with a heterojunction launcher which achieves high-energy electron injection into an active transport region. The potential and limitations for realizing near-ballistic transport in practical device structures under realistic bias conditions are examined. Specific devices considered in this work are charge injection transistors and vertical electron transistors based on lattice-matched AllnAs/GalnAs material systems. Self-consistent Monte Carlo simulations indicate that in order to effectively utilize electron near-ballistic transport for achieving improved performances, the device structure and operating conditions must be properly designed.}, number={5S}, journal={Semiconductor Science and Technology}, publisher={IOP Publishing}, author={Tian, H and Kim, K W and Littlejohn, M A and Woolard, D L}, year={1994}, month={May}, pages={824–827} }
 @article{woolard_tian_littlejohn_kim_1994, title={Efficient ohmic boundary conditions for the Monte Carlo simulation of electron transport}, volume={41}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.278516}, DOI={10.1109/16.278516}, abstractNote={The development of macroscopic transport models, accurate for studying hot-electron transport in semiconductors, involves a direct consideration of higher-moment terms. All hydrodynamic transport models (HTM's), derived from moments of the Boltzmann transport equation, require the introduction of closure relations to terminate the resulting infinite set of macroscopic equations. These closure relations are used as analytical approximations to distributional-dependent integral coefficients. The most popular theoretical approach employed for the construction and evaluation of these higher-moment transport-parameter closures is the Monte Carlo (MC) method. Since the MC method is computationally intensive, the discovery and implementation of efficient MC modeling techniques (either numerical or physical) is of significant value. This paper reports on a relationship between device boundary conditions and the convergence range of higher-moment terms in time-independent MC simulations. Specifically, a set of ohmic BC's which offer computational advantages is presented. This particular mathematical approach, which allows for two degrees of freedom, is shown to be more efficient in generating the full electron distribution function than conventional BC methods (i.e., strictly equilibrium-based). >}, number={4}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Woolard, D.L. and Tian, Hong and Littlejohn, M.A. and Kim, K.W.}, year={1994}, month={Apr}, pages={601–606} }
 @article{yu_kim_stroscio_iafrate_ballato_1994, title={Electron–acoustic-phonon scattering rates in rectangular quantum wires}, volume={50}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.50.1733}, DOI={10.1103/PhysRevB.50.1733}, abstractNote={Electron--acoustic-phonon scattering in a rectangular quantum wire is studied. The Hamiltonian describing the deformation-potential interaction of confined acoustic phonons with carriers is derived by quantizing the appropriate, experimentally verified approximate compressional acoustic-phonon modes in a free-standing rectangular quantum wire. The scattering rate due to the deformation-potential interaction is obtained for GaAs quantum wires with a range of cross-sectional dimensions. The results demonstrate that a proper treatment of confined acoustic phonons may be essential to correctly model electron scattering rates at low energies in nanoscale structures.}, number={3}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Yu, SeGi and Kim, K. W. and Stroscio, Michael A. and Iafrate, Gerald J. and Ballato, Arthur}, year={1994}, month={Jul}, pages={1733–1738} }
 @article{stroscio_kim_1994, title={Generalized piezoelectric scattering rate for electrons in a two-dimensional electron gas}, volume={37}, ISSN={0038-1101}, url={http://dx.doi.org/10.1016/0038-1101(94)90123-6}, DOI={10.1016/0038-1101(94)90123-6}, abstractNote={This paper deals with the quantization of the acoustic modes in nanomechanical systems with coupled acoustic and electromagnetic modes in piezoelectric structures. Specifically, the well-known Bleustein-Gulyaev (BG) modes in the theory of surface acoustic wave devices, are second quantized so that the relationship between the acoustic modes and the electromagnetic modes can be examined in the limit where the acoustic mode is a single acoustic phonon. By considering a theory where the quantized acoustic phonons are explicitly related to the electromagnetic modes, this treatment allows a description of nanomechanical systems where acoustic and electromagnetic modes can be described in the nanoscale limit. This effort will examine quantitatively the electromagnetic-acoustic interaction caused by the piezoelectricity in the limit where the classical acoustic waves must be described in terms of phonons.}, number={1}, journal={Solid-State Electronics}, publisher={Elsevier BV}, author={Stroscio, Michael A. and Kim, K.W.}, year={1994}, month={Jan}, pages={181–182} }
 @article{erdoǧan m. u._sankaran_kim_stroscio_iafrate_1994, title={Phonon-assisted Γ-Xtransition rates in type-II superlattices}, volume={50}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.50.2485}, DOI={10.1103/PhysRevB.50.2485}, abstractNote={The \ensuremath{\Gamma}-X transition rate for electrons in type-II superlattices is calculated for the case of optical-phonon emission. The tight-binding method for electronic band structure and the dielectric continuum model for phonons are used. The relative strength of scattering due to different phonon modes is examined for varying superlattice dimensions. The scattering rate is highest when the energy separation between the \ensuremath{\Gamma} and X levels is smallest, and decreases quickly as the separation increases. It is found that the strongest scattering rate is due to the emission of AlAs confined modes. Changing of parity with layer thickness and its effect on scattering are discussed.}, number={4}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Erdoǧan M. U. and Sankaran, V. and Kim, K. W. and Stroscio, M. A. and Iafrate, G. J.}, year={1994}, month={Jul}, pages={2485–2491} }
 @article{stroscio_kim_yu_ballato_1994, title={Quantized acoustic phonon modes in quantum wires and quantum dots}, volume={76}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.357305}, DOI={10.1063/1.357305}, abstractNote={Acoustic phonon modes in isotropic cubic media are derived for a number of quantum-wire and quantum-dot geometries of significant interest in nanoelectronics and optoelectronics. In each case, the mode amplitude is determined by requiring that the mode energy be given by that of the properly quantized phonon. For the case of cylindrical quantum wires and quantum dots with rectangular faces, the Hamiltonians for the deformation potential interactions are derived. These quantized acoustic modes and the associated deformation potential Hamiltonians provide a basis for modeling carrier-acoustic-phonon interactions in a variety of mesoscopic devices. Our new results supplement previous treatments of related piezoelectric effects in cylindrical quantum wires.}, number={8}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Stroscio, Michael A. and Kim, K. W. and Yu, SeGi and Ballato, Arthur}, year={1994}, month={Oct}, pages={4670–4675} }
 @inproceedings{erdogan_sankaran_kim_stroscio_iafrate_1994, title={Real-space transfer of photoexcited electrons in type-II superlattices via optical-phonon emission}, url={http://dx.doi.org/10.1117/12.178540}, DOI={10.1117/12.178540}, abstractNote={The (Gamma) -X scattering rate of electrons in type-II superlattices by optical-phonon emission is calculated. The tight binding method for electronic band structure and the dielectric continuum model for phonons are used. The relative strength of scattering due to different phonon modes is examined for varying superlattice dimensions. The scattering rate is highest when the energy separation between the (Gamma) and X levels is smallest, and decreases quickly as the separation increases. It is found that the strongest scattering rate is due to the emission of AlAs confined modes. Changing of parity with layer thickness and its effect on scattering are discussed.}, booktitle={Physics and Simulation of Optoelectronic Devices II}, publisher={SPIE}, author={Erdogan, M. U. and Sankaran, V. and Kim, Ki Wook and Stroscio, Michael A. and Iafrate, Gerald J.}, editor={Chow, Weng W. and Osinski, MarekEditors}, year={1994}, month={Jun} }
 @article{woolard_tian_littlejohn_kim_1994, title={The implementation of physical boundary conditions in the Monte Carlo simulation of electron devices}, volume={13}, ISSN={0278-0070}, url={http://dx.doi.org/10.1109/43.317467}, DOI={10.1109/43.317467}, abstractNote={This paper investigates the problem of specifying and implementing physical boundary conditions for the Monte Carlo (MC) simulation of electron dynamics in semiconductor devices. The goal of this work is to establish an accurate and efficient ohmic boundary condition scheme for use in characterizing realistic device structures. In this work, three distinct physical models for specifying the boundary electrons at the ideal ohmic contacts of an N/sup +/-N-N/sup +/ GaAs Ballistic diode structure are investigated. This study demonstrates that a displaced Maxwellian scheme, which allows for an electron ensemble with momentum space displacement and random spread, presents definite computational advantages when one is interested in resolving asymmetries in the electron distribution function throughout the semiconductor device structure. >}, number={10}, journal={IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Woolard, D.L. and Tian, H. and Littlejohn, M.A. and Kim, K.W.}, year={1994}, pages={1241–1246} }
 @article{bhatt_kim_stroscio_1994, title={Theoretical calculation of longitudinal‐optical‐phonon lifetime in GaAs}, volume={76}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.358498}, DOI={10.1063/1.358498}, abstractNote={The anharmonic decay of longitudinal-optical (LO) phonons in zinc-blende semiconductors has been studied. Based on an approach in which the anharmonic crystal potential is estimated using the theory of elasticity, the lifetime of LO phonons via emission of two acoustic phonons is calculated as a function of lattice temperature and phonon wave vector. Application of this model to bulk GaAs shows an excellent agreement with available experimental data. Since the parameters employed in the model can be obtained experimentally, the approach provides a useful tool to investigate LO-phonon lifetimes in semiconductors.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhatt, A. R. and Kim, K. W. and Stroscio, M. A.}, year={1994}, month={Sep}, pages={3905–3907} }
 @article{kaneto_kim_littlejohn_1993, title={A comparison of minority electron transport in In0.53Ga0.47As and GaAs}, volume={63}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.109746}, DOI={10.1063/1.109746}, abstractNote={The electron transport properties of heavily doped p-type In0.53Ga0.47As and GaAs have been investigated and the applications in heterojunction bipolar transistors (HBTs) are emphasized. Using the dielectric function formalism, we have characterized minority electron transport in terms of mean-free path and diffusivity. These parameters quantify the nonequilibrium (ballistic) and near-equilibrium (diffusive) transport in the p-type base region of HBTs. Our calculations demonstrate that electron energies above 300 meV provide no benefit for ballistic transport in p-type InGaAs in terms of momentum relaxation mean-free path. Especially for very heavily doped cases (∼1020 cm−3), low-energy electron injection into the p-type InGaAs base is more advantageous for base transport, as well as the succeeding transport in the base-collector depletion region. When diffusive transport is dominant, p-type InGaAs exhibits superior performance over GaAs for a wide range of doping concentrations.}, number={1}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kaneto, T. and Kim, K. W. and Littlejohn, M. A.}, year={1993}, month={Jul}, pages={48–50} }
 @article{kaneto_kim_littlejohn_1993, title={Calculation of minority-carrier mobilities in heavily dopedp-type semiconductors in the dielectric-function formalism}, volume={47}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.47.16257}, DOI={10.1103/PhysRevB.47.16257}, abstractNote={An alternative approach for the calculation of minority-carrier mobilities is proposed. This approach is based on the self-consistent-field (SCF) method, and it combines elementary excitation theory with an appropriate transport theory beyond the relaxation-time approximation. Detailed information on elementary excitations of majority holes at finite temperature is obtained from the spectral density function (Im[-1/e(q,ω)]) derived by the SCF method. Also, the finite lifetime of holes has been incorporated and a suitable form for the coupling of longitudinal-optical phonons, plasmons, and single-particle excitations is described. We have calculated minority-carrier mobilities for p-type GaAs and p-type Si, which show excellent agreement with available experimental data for a wide range of hole concentrations}, number={24}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kaneto, T. and Kim, K. W. and Littlejohn, M. A.}, year={1993}, month={Jun}, pages={16257–16266} }
 @article{tian_kim_littlejohn_mishra_1993, title={Characteristics of In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As/InP HEMT's with n-and p-channel doping}, volume={40}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.249489}, DOI={10.1109/16.249489}, abstractNote={The effects of modified n- and p-channel doping on the characteristics of 0.25- mu m In/sub 0.52/Al/sub 0.48/As/In/sub 0.53/Ga/sub 0.47/As/InP HEMTs are studied. The introduction of n- or p-channel doping (in addition to the modulation doping in the donor supply layer) is intended to modify the potential well and carrier distribution in the device channel for improved device performance. Self-consistent Monte Carlo simulations and experimental results both show considerably reduced output conductance and increased transconductance for the HEMT using modified p-channel doping compared with those for the HEMT with a modified n-channel. The performance enhancement for the HEMT with modified p-channel doping is attributed to improved carrier confinement in the potential well of the channel and reduced spread in the channel electric field profile. >}, number={12}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Tian, H. and Kim, K.W. and Littlejohn, M.A. and Mishra, U.K.}, year={1993}, pages={2362–2365} }
 @article{woolard_tian_littlejohn_kim_trew_ieong_tang_1993, title={Construction of higher‐moment terms in the hydrodynamic electron‐transport model}, volume={74}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.355189}, DOI={10.1063/1.355189}, abstractNote={A critical step in the development of all hydrodynamic transport models (HTMs), derived from moments of the Boltzmann transport equation, is the introduction of accurate closure relations to terminate the resulting infinite set of macroscopic equations. In general, there are a number of resulting integral terms that are highly dependent on the form of the true electron distribution function. The so-called heat flux term is one very important higher-moment term that requires attention. Methods for the accurate construction of an improved heat-flux model are presented. In this construction, a higher-moments approach is combined with a unique definition of electron temperature (i.e., based upon an ansatz distribution) to investigate the effects of conduction-band nonparabolicity and distributional asymmetry. The Monte Carlo method has been used to evaluate the resulting model closures and to study microscopic electron dynamics. These investigations have identified an important relationship between a particular symmetric (i.e., thermal) component of the electron distribution function and the heat flow vector. This knowledge is important because all the parameters in the HTM must be closed (i.e., related to each other through a common set of system variables) before the technique can be accurately applied to the study of electron transport in semiconductor devices.}, number={10}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Woolard, D. L. and Tian, H. and Littlejohn, M. A. and Kim, K. W. and Trew, R. J. and Ieong, M. K. and Tang, T. W.}, year={1993}, month={Nov}, pages={6197–6207} }
 @article{erdoğan_kim_stroscio_1993, title={Effects of band mixing on hole tunneling times in GaAs/AlAs double‐barrier heterostructures}, volume={62}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.108699}, DOI={10.1063/1.108699}, abstractNote={The tunneling time of holes in GaAs/AlAs double-barrier heterostructures is calculated within the envelope function approximation, including band-mixing effects. The phase delay time is obtained from the energy derivative of the total phase shift of the wave function upon tunneling. The results show clearly that mixing plays a very important role in hole tunneling. In particular, our study suggests that the conventional effective mass models (without band mixing) can significantly overestimate the heavy hole tunneling time and thus are not suitable for estimation of the hole tunneling time. It is also demonstrated that the effect of band mixing on hole tunneling times becomes more important for thicker barriers.}, number={12}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Erdoğan, M. U. and Kim, K. W. and Stroscio, M. A.}, year={1993}, month={Mar}, pages={1423–1425} }
 @article{erdoğan_kim_stroscio_dutta_1993, title={Extension of the Kronig–Penney model for Γ‐Xmixing in superlattices}, volume={74}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.354349}, DOI={10.1063/1.354349}, abstractNote={An extension of the Kronig–Penney model to treat mixings of different valleys in superlattices is presented. The value of the mixing parameter α used in the model is deduced by comparison with more sophisticated theory and various experiments for the GaAs/AlAs material system. It is shown that with the use of a single value for the mixing parameter, this simple and efficient model can reasonably reproduce the important aspects of valley mixing effects in GaAs/AlAs superlattices over a wide range of layer thicknesses.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Erdoğan, M. U. and Kim, K. W. and Stroscio, M. A. and Dutta, M.}, year={1993}, month={Oct}, pages={4777–4779} }
 @article{tian_kim_littlejohn_1993, title={Novel charge injection transistors with heterojunction source (launcher) and drain (blocker) configurations}, volume={63}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.110390}, DOI={10.1063/1.110390}, abstractNote={The results of a theoretical study of novel charge injection transistors (CHINTs) with heterojunction source and drain are presented. The proposed device structures employ a wide band-gap (with respect to the channel) material as the device source and/or drain regions, in contrast to the conventional, homojunction source (drain) CHINT structure. It is demonstrated that the spatial location of real-space transfer (RST) is strongly dependent on the initial energy of injected electrons in these devices. The introduction of source and drain heterojunctions serves for enhancing the RST effect and for the blocking electrons which constitute leakage current. Results from two-dimensional, self-consistent ensemble Monte Carlo simulations reveal that the proposed CHINTs feature increased current drive capability, reduced drain leakage current, and faster switching speed.}, number={2}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Tian, H. and Kim, K. W. and Littlejohn, M. A.}, year={1993}, month={Jul}, pages={174–176} }
 @article{stroscio_kim_1993, title={Piezoelectric scattering of carriers from confined acoustic modes in cylindrical quantum wires}, volume={48}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.48.1936}, DOI={10.1103/PhysRevB.48.1936}, abstractNote={Confined acoustic modes are derived for a free-standing nanometer-scale cylindrical polar semiconductor quantum wire. The piezoelectric scattering Hamiltonian is calculated for the interaction of charge carriers with the lowest-order azimuthally symmetric torsional modes in such nanometer-scale quantum wires}, number={3}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Stroscio, Michael A. and Kim, K. W.}, year={1993}, month={Jul}, pages={1936–1938} }
 @article{bhatt_kim_stroscio_iafrate_dutta_grubin_haque_zhu_1993, title={Reduction of interface phonon modes using metal‐semiconductor heterostructures}, volume={73}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.353139}, DOI={10.1063/1.353139}, abstractNote={Based on a simplified analysis of perfectly conducting metals, it has been suggested qualitatively that establishing metal-semiconductor interfaces at the heterojunctions of polar semiconductor quantum wells introduces a set of boundary conditions that dramatically reduces or eliminates unwanted carrier energy loss caused by interactions with interface longitudinal-optical (LO) phonon modes. In this article, it is theoretically demonstrated that comparable reductions in LO phonon scattering strengths may be achieved for metal-semiconductor structures with metal having realistic conductivities and Thomas–Fermi screening lengths.}, number={5}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Bhatt, A. R. and Kim, K. W. and Stroscio, M. A. and Iafrate, G. J. and Dutta, Mitra and Grubin, Harold L. and Haque, Reza and Zhu, X. T.}, year={1993}, month={Mar}, pages={2338–2342} }
 @article{bhatt_kim_stroscio_higman_1993, title={Simplified microscopic model for electron–optical-phonon interactions in quantum wells}, volume={48}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.48.14671}, DOI={10.1103/PhysRevB.48.14671}, abstractNote={A simplified microscopic model of optical phonons in dimensionally confined structures is formulated and applied to calculate electron-optical-phonon scattering rates in GaAs/AlAs quantum wells. For this simplified model which circumvents performing a complicated ab initio calculation of the force constants at the interface, it is demonstrated that the resulting dispersion relation and scattering rates for electron-optical-phonon interactions agree very well with those obtained from detailed ab initio studies. It is also shown that for GaAs/AlAs structures, the macroscopic dielectric continuum model provides a good approximation to the scattering rate predicted by the microscopic models}, number={19}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Bhatt, A. R. and Kim, K. W. and Stroscio, M. A. and Higman, J. M.}, year={1993}, month={Nov}, pages={14671–14674} }
 @article{sarma_campos_stroscio_kim_1992, title={Confined phonon modes and hot-electron energy relaxation in semiconductor microstructures}, volume={7}, ISSN={0268-1242 1361-6641}, url={http://dx.doi.org/10.1088/0268-1242/7/3b/015}, DOI={10.1088/0268-1242/7/3b/015}, abstractNote={The role of confined phonon modes in determining the energy relaxation of hot electrons in low-dimensional semiconductor microstructures is discussed within a dielectric continuum model for the LO phonon confinement and a long wavelength Frohlich model for the electron-phonon interaction. Numerical results are provided for the hot-electron relaxation rate as a function of electron temperature and density for GaAs quantum wells and quantum wires by taking into account emission of slab phonon modes. Comparison with existing experimental results shows some evidence for slab phonon emission in intersubband electronic relaxation in reasonably narrow quantum wells. It is argued that most experiments can be interpreted in terms of an electron-bulk phonon interaction model (i.e. by taking into account the effect of confinement only on the electrons and assuming the phonons to be the usual bulk three-dimensional phonons) because a number of important physical processes, such as screening, the hot phonon effect, phonon self-energy correction etc, make it difficult to distinguish quantitatively between various models for phonon confinement, except perhaps in the narrowest (<50 AA) wells and wires. Detailed numerical results for the calculated intra-subband relaxation rate in GaAs quantum wires are provided within the slab phonon and the electron temperature model, including the effects of dynamical screening, quantum degeneracy and nonequilibrium hot phonons.}, number={3B}, journal={Semiconductor Science and Technology}, publisher={IOP Publishing}, author={Sarma, S Das and Campos, V B and Stroscio, M A and Kim, K W}, year={1992}, month={Mar}, pages={B60–B66} }
 @article{kaneto_kim_littlejohn_1992, title={Dielectric response functions of heavily doped zincblende semiconductors with finite particle lifetime}, volume={72}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.352222}, DOI={10.1063/1.352222}, abstractNote={The dielectric response functions in the valence bands and in the conduction band of heavily doped zincblende semiconductors have been evaluated using the self-consistent field method and incorporating the finite lifetime of particles in the relaxation time approximation. Scattering rates of injected electrons are calculated with the Born approximation in the dielectric response function formalism at finite temperature. The finite particle lifetime introduces significant modifications to the spectral density function {Im[−1/ε(q,ω)]} at small q, where collective excitations (i.e., coupled phonon-plasmon modes) are heavily damped due to collisions. However, these modifications are small at large q. At the same time, the scattering rates of injected electrons are strongly affected by the temperature dependence of these effects, which are particularly significant for p-type semiconductors.}, number={9}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kaneto, T. and Kim, K. W. and Littlejohn, M. A.}, year={1992}, month={Nov}, pages={4139–4147} }
 @article{stroscio_kim_iafrate_dutta_grubin_1992, title={Dramatic reduction in the longitudinal-optical phonon emission rate in polar-semiconductor quantum wires}, volume={65}, ISSN={0950-0839 1362-3036}, url={http://dx.doi.org/10.1080/09500839208207532}, DOI={10.1080/09500839208207532}, abstractNote={Abstract Novel quantum-effect polar-semiconductor structures underlie technologies portending dramatic enhancements in the capability to process information orders of magnitude faster than is possible currently. In many embodiments of these quantum-effect structures, charges are transported in quasi-one-dimensional quantum wires which must support the transport of charges at high mobilities. However, it has recently been demonstrated that the longitudinal-optical (LO) phonons established at quantum-wire interfaces lead to dramatic enhancements in carrier-phonon interactions and concomitant degradation in carrier mobility. This letter demonstrates that phonon modes may be tailored through the judicious use of metal-semiconductor interfaces in such a way as to dramatically reduce unwanted emission of interface LO phonons and, consequently, to lead to the achievement of high quantum-wire mobility.}, number={4}, journal={Philosophical Magazine Letters}, publisher={Informa UK Limited}, author={Stroscio, Michael A. and Kim, K. W. and Iafrate, Gerald J. and Dutta, Mitra and Grubin, Harold L.}, year={1992}, month={Apr}, pages={173–176} }
 @inproceedings{mishra_jelloian_lui_thompson_rosenbaum_kim_1992, title={Effect of N-Channel and P-Channel doping on the IV characteristics of Alinas-Gainas hemts}, volume={120}, booktitle={Institute of Physics Conference Series}, author={Mishra, U.K and Jelloian, L.M. and Lui, M. and Thompson, M and Rosenbaum, S.E. and Kim, K.W.}, year={1992}, pages={287–292} }
 @article{tian_kim_littlejohn_mishra_hashemi_1992, title={Effects of doping variations on electron transport in GaAsn+‐n‐n+structures}, volume={72}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.351920}, DOI={10.1063/1.351920}, abstractNote={Electron transport properties in GaAs n+-n-n+ structures with varying doping profiles (in the direction of electron transport) are investigated using self-consistent ensemble Monte Carlo simulations. In particular, we study the effects of ramp doping [i.e., linearly increasing (ramp-up) or decreasing (ramp-down) doping density within the n region] and spike doping (i.e., introducing one or more n+ spikes in the n region) on electron transport to assess differences, advantages, and potential applications of these doping profiles on device performance. Underlying physical mechanisms for electron transport in these structures are analyzed. Simulation results reveal that overall electron transport can be improved significantly by employing ramp-up (rather than ramp-down) doping and multispike (instead of single-spike) doping schemes. Potential advantages of variable doping in field-effect transistor applications include enhanced current drive capability, reduced source resistance, and improved breakdown characteristics.}, number={12}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Tian, H. and Kim, K. W. and Littlejohn, M. A. and Mishra, U. K. and Hashemi, M.}, year={1992}, month={Dec}, pages={5695–5701} }
 @article{kim_bhatt_stroscio_turley_teitsworth_1992, title={Effects of interface phonon scattering in multiheterointerface structures}, volume={72}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.351569}, DOI={10.1063/1.351569}, abstractNote={In this paper, the commonly used but idealistic formulation of quantized optical-phonon modes for a heterostructure system with only two heterojunctions (i.e., single quantum-well structures) is extended to the more realistic case of multiheterointerface structures. By applying the macroscopic dielectric continuum approach, dispersion relations and interaction Hamiltonians for interface-phonon modes are derived for a double-barrier structure and scattering rates based on these results are used to determine the range of practical validity of the idealistic model using interaction Hamiltonians appropriate for single quantum wells with infinite barrier widths. It is found that when the dimensions of the structures are larger than approximately 30 Å, this simplified description can be applied to multiheterointerface structures in general with reasonable accuracy.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kim, K. W. and Bhatt, A. R. and Stroscio, Michael A. and Turley, P. J. and Teitsworth, S. W.}, year={1992}, month={Sep}, pages={2282–2287} }
 @article{mickevicius_mitin_kim_stroscio_1992, title={Electron high-field transport in multisubband quantum wire structures}, volume={7}, ISSN={0268-1242 1361-6641}, url={http://dx.doi.org/10.1088/0268-1242/7/3B/074}, DOI={10.1088/0268-1242/7/3B/074}, abstractNote={The Monte Carlo simulation of electron transport in multisubband quasi-one-dimensional GaAs/AlAs quantum wires (QWIs) are presented. The electron intrasubband and intersubband scattering by surface-optical and confined longitudinal-optical phonons in QWIs has been included in the program. It is demonstrated that at room temperature the electron drift velocity in the QWI is suppressed by electron intersubband scattering and does not exceed the bulk material values. The energy dependence of the total scattering rate in ideal QWIs exhibits multiple sharp peaks related to intersubband transitions. The scattering rates in the real QWIs with variable thicknesses are calculated as well. The results show that even small variation in thickness leads to a significant broadening of the very first peaks and complete washing-out of the peak-like structure at higher energies.}, number={3B}, journal={Semiconductor Science and Technology}, publisher={IOP Publishing}, author={Mickevicius, R and Mitin, V V and Kim, K W and Stroscio, M A}, year={1992}, month={Mar}, pages={B299–B301} }
 @article{mickevicius_mitin_kim_stroscio_iafrate_1992, title={Electron intersubband scattering by confined and localized phonons in real quantum wires}, volume={4}, ISSN={0953-8984 1361-648X}, url={http://dx.doi.org/10.1088/0953-8984/4/21/011}, DOI={10.1088/0953-8984/4/21/011}, abstractNote={The present study deals with electron intersubband scattering in real quantum wire structures. Both the multi-subband structure and confined phonon modes are considered together. The rates of scattering by confined longitudinal-optical (LO) phonons and by surface-optical (SO) phonons are calculated taking into account all possible LO phonon modes as well as all possible electron intersubband transitions. The estimations of transition rates for GaAs/AlAs QWIS have shown that intrasubband electron scattering and most intersubband transitions are due primarily to scattering by confined LO phonons, but in resonant intersubband transitions the contribution of SO phonons may be dominant when the phonon energy is close to the intersubband energy separation. Moreover, electron-SO-phonon scattering might play an important part in low-temperature electron transport because the GaAs-like SO mode is shifted towards lower frequencies compared with that of LO phonons. The energy dependence of the total scattering rate in an ideal quantum wire exhibits multiple sharp peaks related to each intersubband transition. These peaks originate from the resonant nature of the density of states in ideal one-dimensional systems. It is demonstrated that in real quantum wires with variable thickness the resonant peaks broaden or even disappear due to variation of subband energies.}, number={21}, journal={Journal of Physics: Condensed Matter}, publisher={IOP Publishing}, author={Mickevicius, R and Mitin, V V and Kim, K W and Stroscio, M A and Iafrate, G J}, year={1992}, month={May}, pages={4959–4970} }
 @article{mickevicius_mitin_kim_stroscio_1992, title={Electron intersubband scattering in real quantum wires}, volume={11}, ISSN={0749-6036}, url={http://dx.doi.org/10.1016/0749-6036(92)90380-N}, DOI={10.1016/0749-6036(92)90380-N}, abstractNote={The rates of electron intra- and intersubband scattering by surface optical (SO) and confined longitudinal optical (LO) phonons in quasi-one-dimensional GaAs/AlAs quantum wires (QWIs) are calculated. It is shown that electron-SO-phonon intersubband scattering can be resonant, so that the scattering rate tends to infinity when intersubband energy separation approaches SO phonon energy. The energy dependence of the total scattering rate in ideal QWIs exhibits multiple sharp peaks related to intersubband transitions. The scattering rates in the real QWIs with variable thickness are calculated. The results show that even small variation in thickness leads to the significant broadening of the very first peaks and complete washing-out of the peak-like structure at higher energies. Monte Carlo simulations of electron transport in the QWI have been performed. It is demonstrated that electron drift velocity in the QWI is considerably suppressed by electron intersubband scattering and is considerably lower than the bulk material values. The role of SO phonons in electron energy dissipation is discussed.}, number={3}, journal={Superlattices and Microstructures}, publisher={Elsevier BV}, author={Mickevicius, R. and Mitin, V.V. and Kim, K.W. and Stroscio, Michael A.}, year={1992}, month={Jan}, pages={277–280} }
 @article{kim_tian_kim_littlejohn_1992, title={Electron velocity‐field characteristics of In0.52Al0.48As}, volume={61}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.107594}, DOI={10.1063/1.107594}, abstractNote={Theoretical results of electron transport in n-type In0.52Al0.48As are presented. The transport properties of this important semiconductor were obtained using the Monte Carlo method. In particular, velocity-electric field characteristics for different temperatures and doping concentrations in bulk In0.52Al0.48As are calculated for the first time. Physical parameters for In0.52Al0.48As (which is lattice-matched to InP and In0.53Ga0.47As) were obtained based on interpolation of available experimental and theoretical results for InAs, AlAs, and In0.75Al0.25As. Our study suggests that In0.52Al0.48As has electron transport properties which are comparable to and complimentary with those of other materials lattice-matched to InP.}, number={10}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kim, H. S. and Tian, H. and Kim, K. W. and Littlejohn, M. A.}, year={1992}, month={Sep}, pages={1202–1204} }
 @inproceedings{tian_kim_littlejohn_mishra_hashemi_nasecode_1992, title={Ensemble Monte-Carlo simulation of electron-transport in GAAS N+ -N -N+ Structures with laterally varying doping}, booktitle={Proceedings of the 8th International Conference on the Numerical Analysis of Semiconductor Devices and Integrated Circuits}, author={Tian, H and Kim, K.W. and Littlejohn, M.A. and Mishra, U.K. and Hashemi, M. and Nasecode, M., VIII}, year={1992}, pages={125–126} }
 @article{woolard_tian_littlejohn_trew_kim_1992, title={Impact of k-space transfer and band nonparabolicity on electron transport in a GaAs ballistic diode}, volume={7}, ISSN={0268-1242 1361-6641}, url={http://dx.doi.org/10.1088/0268-1242/7/3B/091}, DOI={10.1088/0268-1242/7/3B/091}, abstractNote={The results of studying a submicron GaAs ballistic diode, using a new multi-valley ( Gamma ,L and X) nonparabolic hydrodynamic transport model, are presented. Numerical simulations indicate that accurately including the effects of nonparabolicity in the streaming terms and k-space transfer in the velocity and energy equations is very important in correctly determining the conductance of the device. The existence and amount of negative differential conductance was determined to be strongly influenced by both of these physical factors. Furthermore, the sensitivity of device conductance to changes in the thermal conductivity is diminished significantly when nonparabolicity is accurately incorporated.}, number={3B}, journal={Semiconductor Science and Technology}, publisher={IOP Publishing}, author={Woolard, D L and Tian, H and Littlejohn, M A and Trew, R J and Kim, K W}, year={1992}, month={Mar}, pages={B354–B356} }
 @article{tian_kim_littlejohn_1992, title={Novel heterojunction real-space transfer logic transistor structures: a model-based investigation}, volume={39}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.158787}, DOI={10.1109/16.158787}, abstractNote={Ensemble Monte Carlo simulations are employed in order to explore the feasibility of a novel real-space transfer logic transistor (RSTLT) structure. The operational principles of the proposed RSTLT are based on the concept of hot electron real-space transfer (RST), including the fact that the spatial location of electron RST is determined by applied bias and heterointerface energy barrier height in a multiterminal heterojunction microstructure. The results of two-dimensional, self-consistent steady-state and transient simulations demonstrate that the proposed RSTLT features ultrafast current switching which can be used to realize NOT/EQUIVALENT logic functions in a single heterojunction device. The logic operation is easily extended to NOR/AND functions. A conservative estimate of the characteristic delay time for current switching is approximately 3 ps in the proposed RSTLT structure. >}, number={10}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Tian, H. and Kim, K.W. and Littlejohn, M.A.}, year={1992}, pages={2189–2196} }
 @article{qiang_pollak_sotomayor torres_leitch_kean_stroscio_iafrate_kim_1992, title={Size dependence of the thermal broadening of the exciton linewidth in GaAs/Ga0.7Al0.3As single quantum wells}, volume={61}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.107554}, DOI={10.1063/1.107554}, abstractNote={We have studied the temperature dependence of the linewidth, Γ(T), of the fundamental absorption edge in bulk GaAs and four GaAs/Ga0.7Al0.3As single quantum wells of different well width using photoreflectance. As a result of the size dependence of the exciton-longitudinal optical phonon interaction, the thermal broadening of the linewidth diminishes as the dimensionality and size of the system are reduced.}, number={12}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Qiang, H. and Pollak, Fred H. and Sotomayor Torres, C. M. and Leitch, W. and Kean, A. H. and Stroscio, Michael A. and Iafrate, Gerald J. and Kim, K. W.}, year={1992}, month={Sep}, pages={1411–1413} }
 @article{kim_littlejohn_stroscio_iafrate_1992, title={Transition from LO-phonon to SO-phonon scattering in mesoscale structures}, volume={7}, ISSN={0268-1242 1361-6641}, url={http://dx.doi.org/10.1088/0268-1242/7/3B/013}, DOI={10.1088/0268-1242/7/3B/013}, abstractNote={Macroscopic dielectric continuum models of optical-phonon modes predict enhancements in the magnitudes of the surface-optical (SO) modes in double-barrier heterostructures as the heterojunction-to-heterojunction separation is reduced. In this paper, the ratio of electron scattering by the SO-phonon modes to that by the (electrostatic) confined longitudinal-optical- (LO-) phonon modes is calculated for a GaAs/AlAs short-period superlattice based on the assumption that electron-SO-phonon scattering may be described by a scalar potential. The scaling of the ratio of electron-SO-phonon scattering to electron-LO-phonon scattering as a function of the superlattice period provides a sensitive test of the appropriateness of the scalar-potential model. The effect of phonon confinement on electron-optical-phonon scattering rates is presented for rectangular quantum wires as well. A major conclusion of these new results is that it is essential to model phonon confinement properly in predicting carrier transport properties in mesoscale structures.}, number={3B}, journal={Semiconductor Science and Technology}, publisher={IOP Publishing}, author={Kim, K W and Littlejohn, M A and Stroscio, M A and Iafrate, G J}, year={1992}, month={Mar}, pages={B49–B51} }
 @article{tian_kim_littlejohn_bedair_witkowski_1992, title={Two-dimensional analysis of short-channel delta-doped GaAs MESFETs}, volume={39}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.155870}, DOI={10.1109/16.155870}, abstractNote={Key design parameters for delta-doped GaAs MESFETs, such as delta doping profile, top layer background doping density, and scaling of lateral feature size, are investigated using a two-dimensional numerical simulation. A three-region (delta-doped conducting channel, top layer, and substrate) velocity-field relation is implemented in the model as appropriate for the particular device structure which is simulated. Simulation results show excellent agreement with a fabricated 0.5- mu m gate-length delta-doped GaAs MESFETs based on atomic layer epitaxy material. An extrinsic transconductance of 370 mS/mm and a drain-source current of 270 mA/mm are obtained for typical devices, and the maximum transconductance is as high as 400 mS/mm. These are the best DC results yet reported for 0.5- mu m gate-length delta-doped GaAs MESFETs. Considerations of design and optimization are discussed in terms of threshold voltage sensitivity, transconductance, current drive capability, and cutoff frequency, based on both simulation and experiment results. >}, number={9}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Tian, H. and Kim, K.W. and Littlejohn, M.A. and Bedair, S.M. and Witkowski, L.C.}, year={1992}, pages={1998–2006} }
 @article{tian_kim_littlejohn_1991, title={An investigation of the effects of doping profile variations on AlGaAs/GaAs high electron mobility transistor performance}, volume={70}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.349096}, DOI={10.1063/1.349096}, abstractNote={We present results from a theoretical study of the influence of doping profile variations on the performance of delta-doped AlGaAs/GaAs high electron mobility transistors (HEMTs). An ensemble Monte Carlo simulation coupled with a self-consistent solution of the two-dimensional Poisson equation is used to investigate HEMTs which employ both single and double delta-doped profiles with varying doping configurations. The calculated results reveal that single delta-doped HEMTs designed with identical threshold voltages exhibit improved device behavior when thinner delta-doped layers with more heavily doped concentrations are utilized. For double delta-doped HEMTs with an identical total doping in the AlGaAs layer, improved threshold voltage control is obtained as the spacing between two delta-doped layers increases. However, this increase in spacing also causes a degradation in transconductance, cut-off frequency, and switching time. As gate bias increases, the dependence of device performance (or degradation) on the spacing between doping planes becomes less pronounced due to the upward shift in threshold or ‘‘onset’’ of parallel conduction in the AlGaAs layer.}, number={8}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Tian, H. and Kim, K. W. and Littlejohn, M. A.}, year={1991}, month={Oct}, pages={4593–4600} }
 @article{kim_tian_littlejohn_1991, title={Analysis of delta-doped and uniformly doped AlGaAs/GaAs HEMT's by ensemble Monte Carlo simulations}, volume={38}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.119008}, DOI={10.1109/16.119008}, abstractNote={Transport properties and device performance of delta-doped and uniformly doped AlGaAs/GaAs high electron mobility transistors (HEMTs) with identical threshold voltages and gate capacitors are investigated using two-dimensional self-consistent ensemble Monte Carlo simulations. The model includes the effects of real-space transfer and carrier degeneracy, as well as the influence of DX centers and surface states. A one-to-one comparison of simulation results for the two devices demonstrates superior performance for the delta-doped HEMT and provides a physical basis for the observed improvements. In particular, the delta-doped HEMT maintains its superior device performance as gate bias is increased. Reasons for these improvements are reported. >}, number={8}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Kim, K.W. and Tian, H. and Littlejohn, M.A.}, year={1991}, pages={1737–1742} }
 @article{stroscio_kim_rudin_1991, title={Boundary conditions for electron-LO-phonon interaction in polar semiconductor quantum wires}, volume={10}, ISSN={0749-6036}, url={http://dx.doi.org/10.1016/0749-6036(91)90147-J}, DOI={10.1016/0749-6036(91)90147-J}, abstractNote={Abstract The Frohlich Hamiltonian describing the interaction of longitudinal-optical (LO) phonons and charge carriers in a quantum wire have been derived previously by imposing boundary conditions on the electrostatic potential of the phonon field. In this study, the Frohlich Hamiltonian for a quantum wire is derived by taking into account appropriate mechanical boundary conditions and the resulting Hamiltonian is used to calculate the total scattering rate for electron-LO-phonon scattering.}, number={1}, journal={Superlattices and Microstructures}, publisher={Elsevier BV}, author={Stroscio, M.A. and Kim, K.W. and Rudin, S.}, year={1991}, month={Jan}, pages={55–58} }
 @article{kim_stroscio_bhatt_mickevicius_mitin_1991, title={Electron‐optical‐phonon scattering rates in a rectangular semiconductor quantum wire}, volume={70}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.350275}, DOI={10.1063/1.350275}, abstractNote={One-dimensional electron-optical-phonon interaction Hamiltonians in a rectangular quantum wire consisting of diatomic polar semiconductors are derived under the macroscopic dielectric continuum model. The scattering rates calculated in a GaAs square quantum wire show that when the quantum wire is free-standing in vacuum, the interaction by the surface-optical phonon modes is very strong and may dominate over other scattering processes, especially with dimensions of about 100 Å or less. When the wire is embedded in a polar semiconductor (AlAs to be specific), the scattering rates by the surface-optical phonon modes become generally smaller, but yet comparable to those by the confined longitudinal-optical modes as the wire dimension shrinks. A considerable decrease in the total scattering rate for optical phonons as a result of simple reduction in dimensionality is not observed in this study.}, number={1}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kim, K. W. and Stroscio, M. A. and Bhatt, A. and Mickevicius, R. and Mitin, V. V.}, year={1991}, month={Jul}, pages={319–327} }
 @article{woolard_tian_trew_littlejohn_kim_1991, title={Hydrodynamic electron-transport model: Nonparabolic corrections to the streaming terms}, volume={44}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.44.11119}, DOI={10.1103/PhysRevB.44.11119}, abstractNote={This paper presents a hydrodynamic model suitable for studying hot-electron transport in semiconducting materials with nonparabolic conduction bands. The model presented is based upon a unique derivation of the moments of the Boltzmann-transport equation for the streaming (collision-independent) terms. This derivation implements an efficient and compact mathematical formalism appropriate for electrons under the influence of high electric fields and nonstationary conditions. The theoretical investigation also introduces a distributional form with nonparabolic properties to precisely define the resulting nonparabolic streaming parameters. The final set of model equations is exhibited in a fashion to clearly show the correction factors to the more familiar hydrodynamic model applicable for the constant-effective-mass case. In general, the hydrodynamic (or conservation) model contains pure transport terms that are treated as being independent of the specific dissipation mechanisms and collision terms to directly account for the influence of scattering. Since the collision terms are almost always treated phenomenologically using a relaxation-time approximation, our formulation of the streaming terms should significantly improve the overall accuracy of the approach. In addition, this paper presents the results of an extensive investigation of the assumed ansatz distribution and resulting nonparabolic-model parameters using an elaborate Monte Carlo model. The Monte Carlo technique was used to generate comparison electron distributions and exact values for the nonparabolic transport parameters for stationary and nonstationary electronic structures. In all cases, excellent agreement was found between the Monte Carlo--calculated parameters and the derived nonparabolic-model terms. The Monte Carlo calculations also revealed that the ansatz distribution used in the derivation represented a significant improvement over the more familar displaced Maxwellian. Therefore, this model should prove very valuable for studying electronic-device structures operating under high-bias conditions.}, number={20}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Woolard, D. L. and Tian, H. and Trew, R. J. and Littlejohn, M. A. and Kim, K. W.}, year={1991}, month={Nov}, pages={11119–11132} }
 @article{tian_kim_littlejohn_1991, title={Influence ofDXcenters and surface states on δ‐doped high‐electron‐mobility transistor performance}, volume={69}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.348425}, DOI={10.1063/1.348425}, abstractNote={The roles of DX centers and surface states associated with the n-AlGaAs layer of δ-doped AlGaAs/GaAs high-electron-mobility transistors have been investigated by employing a two-dimensional, self-consistent ensemble Monte Carlo simulation. It is found that both DX centers and surface states degrade device performance, particularly as gate-to-source voltage increases. This degradation is manifested largely through reduced channel electron concentration, increased intervalley scattering, and enhanced real-space transfer. Of the two defect states, DX centers have more detrimental influence on drain current and transconductance.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Tian, H. and Kim, K. W. and Littlejohn, M. A.}, year={1991}, month={Apr}, pages={4123–4128} }
 @article{stroscio_iafrate_kim_littlejohn_goronkin_maracas_1991, title={Transition from longitudinal‐optical phonon scattering to surface‐optical phonon scattering in polar semiconductor superlattices}, volume={59}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.106354}, DOI={10.1063/1.106354}, abstractNote={Dielectric continuum models of optical-phonon modes predict an enhancement in the strength of the surface-optical (SO) modes in double-barrier heterostructures as the heterojunction-to-heterojunction separation is reduced. There is currently no consensus on the nature of the electron-SO-phonon coupling interaction. In this work, the ratio of electron scattering by the SO-phonon modes to that by the confined longitudinal-optical (LO) phonon modes is calculated for a GaAs/AlAs short-period superlattice based on the assumption that the electron-SO-phonon interaction may be described by a scalar potential. The scaling of the ratio of electron-SO-phonon scattering to electron-LO-phonon scattering as a function of the superlattice period provides a sensitive test of the appropriateness of the scalar-potential model.}, number={9}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Stroscio, Michael A. and Iafrate, Gerald J. and Kim, K. W. and Littlejohn, M. A. and Goronkin, Herbert and Maracas, George N.}, year={1991}, month={Aug}, pages={1093–1095} }
 @article{kim_stroscio_1990, title={Electron‐optical‐phonon interaction in binary/ternary heterostructures}, volume={68}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.346871}, DOI={10.1063/1.346871}, abstractNote={The macroscopic dielectric continuum model is used to derive electron-optical-phonon interaction Hamiltonians for binary/ternary heterostructures containing both single and double heterointerfaces. The formulation presented in this work leads to a general prescription for the calculation of mode-strength coefficients in ternary-containing heterostructures. An illustration of these results is provided by exhibiting the mode strengths of the interaction Hamiltonians for the interface and the half-space longitudinal optical modes in a GaAs/AlyGa1−yAs single heterostructure.}, number={12}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kim, K. W. and Stroscio, M. A.}, year={1990}, month={Dec}, pages={6289–6292} }
 @inproceedings{kim_stroscio_hall_1990, title={Frequencies of confined longitudinal-optical phonon modes in short-period strained semiconductor superlattices}, url={http://dx.doi.org/10.1117/12.22892}, DOI={10.1117/12.22892}, abstractNote={The theories describing the dispersion of longitudinal-optical (LO) phonon modes and electron-LO-phonon interactions are generalized to include the effects of both strain and confinement in semiconductor superlattices and semiconductor microstructures. In particular, the effects of strain and confinement on LO phonon frequencies are analyzed for short-period strained-layer superlattices as well as for semiconductor microstructures where effective force constants are altered near heterojunction interfaces.}, booktitle={Raman and Luminescence Spectroscopies in Technology II}, publisher={SPIE}, author={Kim, Ki Wook and Stroscio, Michael A. and Hall, Jue}, editor={Adar, Fran and Griffiths, James E.Editors}, year={1990}, month={Nov} }
 @article{kim_stroscio_hall_1990, title={Frequencies of confined longitudinal‐optical phonon modes in GaAs/GaP short‐period strained‐layer superlattices}, volume={67}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.345182}, DOI={10.1063/1.345182}, abstractNote={The linear-chain approximation is used to calculate the spectrum of confined longitudinal-optical (LO) phonon frequencies in short-period strained-layer superlattices. The frequencies for confined LO-phonon modes are reported explicitly for the case of GaAs/GaP short-period strained-layer superlattices grown in the 〈001〉 direction. These results are compared with the few existing experimental measurements for such superlattices.}, number={10}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kim, K. W. and Stroscio, M. A. and Hall, J. C.}, year={1990}, month={May}, pages={6179–6183} }
 @article{stroscio_kim_littlejohn_chuang_1990, title={Polarization eigenvectors of surface-optical phonon modes in a rectangular quantum wire}, volume={42}, ISSN={0163-1829 1095-3795}, url={http://dx.doi.org/10.1103/PhysRevB.42.1488}, DOI={10.1103/PhysRevB.42.1488}, abstractNote={Derivation des vecteurs propres de polarisation et des relations de dispersion des modes de phonons longitudinaux optiques (LO) et des phonons optiques de surface (SO) dans un fil quantique rectangulaire, dans l'approximation du continuum. Comparaison des modes SO et LO confines d'un câble quantique a une section efficace carree a la limite d'un vecteur d'onde de phonon s'annulant suivant l'axe du câble quantique. Dans ce cas, on montre que le mode SO domine le mode LO confine dans l'interaction avec les electrons et doit etre pris en compte dans le calcul de la vitesse de diffusion electron-phonon optique}, number={2}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Stroscio, Michael A. and Kim, K. W. and Littlejohn, Michael A. and Chuang, Hsuhung}, year={1990}, month={Jul}, pages={1488–1491} }
 @article{stroscio_kim_hall_1990, title={Variation in frequencies of confined longitudinal-optical phonon modes due to changes in the effective force constants near heterojunction interfaces}, volume={7}, ISSN={0749-6036}, url={http://dx.doi.org/10.1016/0749-6036(90)90123-O}, DOI={10.1016/0749-6036(90)90123-O}, abstractNote={Abstract A linear-chain model with variable force constants for the couplings at heterojunctions is used to calculate the spectrum of confined longitudinal-optical (LO) phonon frequencies in a short-period strained-layer superlattice. Even for the case of a superlattice with only two atomic monolayers in each superlattice layer, it is demonstrated that the frequencies of confined LO-phonon modes are only weakly dependent on variations in interfacial force constants.}, number={2}, journal={Superlattices and Microstructures}, publisher={Elsevier BV}, author={Stroscio, M.A. and Kim, K.W. and Hall, J.C.}, year={1990}, month={Jan}, pages={115–118} }
 @article{higman_kim_hess_van zutphen_boots_1989, title={Monte Carlo simulation of Si and GaAs avalanche electron emitting diodes}, volume={65}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.342988}, DOI={10.1063/1.342988}, abstractNote={Results of Monte Carlo simulations of Si and GaAs p-n electron emitters are presented. A single-electron Monte Carlo transport simulation is used to obtain the total number, including avalanche multiplication, of electrons which reach the surface of the semiconductor, as well as the fraction of these which overcome the work function and are emitted into the vacuum. The distribution function is obtained, as well as ensemble average of quantities such as the ionization coefficient. The efficiency of the device is calculated as a function of both the work function and the top conducting channel thickness. The potential performance of GaAs devices is explored via the Monte Carlo simulation, and calculated results for the Si device are compared to published experimental data.}, number={3}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Higman, J. M. and Kim, K. and Hess, K. and van Zutphen, T. and Boots, H. M. J.}, year={1989}, month={Feb}, pages={1384–1386} }
 @article{kuzuhara_kim_hess_1989, title={Transient simulation of AlGaAs/GaAs/AlGaAs and AlGaAs/InGaAs/AlGaAs hot-electron transistors}, volume={36}, ISSN={0018-9383}, url={http://dx.doi.org/10.1109/16.21190}, DOI={10.1109/16.21190}, abstractNote={The intrinsic switching characteristics of tunneling hot electron transfer amplifier (THETA) devices has been simulated using a time-dependent ensemble Monte Carlo method. Results which show that there is no significant difference between the switch-on and switch-off times of THETA devices and that these switching times are always larger than the average total transit time through the base and the collector barrier are presented. The choice of the base width is important to determine the base transport factor, but it is not a direct measure of the intrinsic switching speed. The importance of velocity overshoot in the collector barrier region for ultra-high-speed device operation is demonstrated. An improved device structure that leads to subpicosecond switching speeds in the THETA structures is proposed. >}, number={1}, journal={IEEE Transactions on Electron Devices}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Kuzuhara, M. and Kim, K. and Hess, K.}, year={1989}, pages={118–123} }
 @article{kuzuhara_kim_arnold_hess_1988, title={Ballistic electron transport across collector barriers in AlGaAs/GaAs hot‐electron transistors}, volume={52}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.99172}, DOI={10.1063/1.99172}, abstractNote={A Monte Carlo calculation has been performed to simulate the experiment of Heiblum and co-workers [Phys. Rev. Lett. 55, 2200 (1985)], regarding ballistic electron transport and the electron transit time across the AlGaAs collector barrier region in AlGaAs/GaAs tunneling hot-electron transfer amplifier devices. Ballistic transport is proven to be highly probable across a 1000-Å-thick collector barrier under retarding field and hot-electron injection conditions at 4.2 K. Applying accelerating fields in the barrier results in almost negligible ballistic fraction of the transmitted hot electrons because of electron scattering into the satellite valleys. This result seems paradoxical at first sight. However, it is typical for electronic transport in heterolayers and fully consistent with the interpretation of the experiments by Heiblum and co-workers. There exists a negative collector-base bias range which minimizes the collector barrier transit time, corresponding to the condition of large ballistic probability and simultaneously relatively little deceleration of the electrons by the applied retarding field.}, number={15}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kuzuhara, M. and Kim, K. and Arnold, D. and Hess, K.}, year={1988}, month={Apr}, pages={1252–1254} }
 @article{kim_hess_1988, title={Electron transport in AlGaAs/GaAs tunneling hot electron transfer amplifiers}, volume={64}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.341570}, DOI={10.1063/1.341570}, abstractNote={A Monte Carlo code has been developed to study electron transport at 4.2 K in AlGaAs/GaAs tunneling hot electron transfer amplifier devices. Our model includes the effects of coupled plasmon-phonon interaction and the Pauli exclusion principle along with more conventional features. The numerical results demonstrate the existence of nearly ballistic transport in the base and the collector barrier, and confirm that the experiments by Heiblum et al. [Phys. Rev. Lett. 55, 2200 (1985)] indeed measure the exact energy distribution of injected ballistic electrons. The device characteristics such as transfer ratio and transit time have also been investigated in detail and are discussed along with the optimum operating conditions.}, number={6}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kim, K. and Hess, K.}, year={1988}, month={Sep}, pages={3057–3062} }
 @article{kim_hess_1988, title={Ensemble Monte Carlo simulation of semiclassical nonlinear electron transport across heterojunction band discontinuities}, volume={31}, ISSN={0038-1101}, url={http://dx.doi.org/10.1016/0038-1101(88)90041-X}, DOI={10.1016/0038-1101(88)90041-X}, abstractNote={An ensemble Monte Carlo simulation code has been developed to study nonlinear electron transpsort across heterojunction interfaces in strong electric fields. The evolution of electron energy and momentum distribution in space and time has been investigated in detail in two AlGaAs/GaAs single well heterostructures under various operating conditions. It is found that overheating, enhanced energy relaxation, and carrier confinement as a consequence of the structure in real space have a pronounced influence on the energy and momentum distribution. As a result, the energy distribution can have a structure which directly reveals the band structure (of the material). The influence of the structure in real space and the band structure of neighboring layer on the ionization rate is also discussed along with the possibility of a new overshoot effect.}, number={5}, journal={Solid-State Electronics}, publisher={Elsevier BV}, author={Kim, K. and Hess, K.}, year={1988}, month={May}, pages={877–885} }
 @article{kim_hess_capasso_1988, title={Monte Carlo study of electron heating and enhanced thermionic emission by hot phonons in heterolayers}, volume={52}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.99194}, DOI={10.1063/1.99194}, abstractNote={We present a numerical study of the effects of nonthermal phonon distributions on electron transport across heterolayers. For the microscopic analysis of both the electron and phonon dynamics, an ensemble Monte Carlo method has been used which includes a realistic band structure. It is observed that the abrupt energy gain at the heterointerface generates significant perturbations in the phonon distribution through the subsequent relaxation and heats the electron distribution because of the reabsorption of nonequilibrium phonons. The influence of a wide range of operating conditions on hot-phonon effects is also discussed.}, number={14}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kim, Kiwook and Hess, Karl and Capasso, Federico}, year={1988}, month={Apr}, pages={1167–1169} }
 @article{kim_hess_capasso_1988, title={Simulations of nonlinear transport in AlGaAs/GaAs single well heterostructures}, volume={31}, ISSN={0038-1101}, url={http://dx.doi.org/10.1016/0038-1101(88)90293-6}, DOI={10.1016/0038-1101(88)90293-6}, abstractNote={There have been considerable efforts devoted to novel APD structures which take advantage of heterojunctions. Unlike bulk structures, the performance of these devices is based on nonlinear transport perpendicular to heterojuctions and involves details of band structures and bandedge discontinuities. Theoretical investigations (Brennan, 1985, 1986; Osaka and coworkers, 1986) have mostly been devoted to the macroscopic quantities rather than microscopic processes. In this paper, we present a numerical study of nonlinear transport across hterointerfaces in strong electric fields and concerntrate on the details of the energy distribution of electrons.}, number={3-4}, journal={Solid-State Electronics}, publisher={Elsevier BV}, author={Kim, K. and Hess, K. and Capasso, F.}, year={1988}, month={Mar}, pages={349–350} }
 @article{arnold_kim_hess_1987, title={Effects of field fluctuation on impact ionization rates in semiconductor devices due to the discreteness and distribution of dopants}, volume={61}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.338076}, DOI={10.1063/1.338076}, abstractNote={Field fluctuations due to dopants in a p+−n junction have been calculated and used to study the effects on the impact ionization rate with a Monte Carlo simulation. Results are plotted along the direction normal to the interface. We report that the field fluctuations have no effect on the ionization rate in the dead space and a small and spatially delayed effect in the region after the dead space even though the field shows large and rapid fluctuations. A similar ‘‘averaged-out’’ effect is also shown for the average electron energy. The enhancement in the ionization rate due to the field fluctuations which Shockley expected in his pioneering research is shown to be negligibly small.}, number={4}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Arnold, D. and Kim, K. and Hess, K.}, year={1987}, month={Feb}, pages={1456–1459} }
 @article{kim_mason_hess_1987, title={Inclusion of collision broadening in semiconductor electron-transport simulations}, volume={36}, ISSN={0163-1829}, url={http://dx.doi.org/10.1103/PhysRevB.36.6547}, DOI={10.1103/PhysRevB.36.6547}, abstractNote={The collision broadening of electronic states due to interactions with phonons is included in a semiclassical transport calculation for semiconductors. The quasiparticle spectral function is used in the transition rates of a Monte Carlo simulation to study the many-body effects of the interacting electron. The full semiconductor band structure is employed through an empirical nonlocal pseudopotential method and the scattering is calculated in the Fock approximation. We find a significant increase in the high-energy tails of the electronic distribution function when the broadening is included. Comparison is made with a similar calculation employing a simpler electronic model.}, number={12}, journal={Physical Review B}, publisher={American Physical Society (APS)}, author={Kim, K. and Mason, B. A. and Hess, K.}, year={1987}, month={Oct}, pages={6547–6550} }
 @article{kim_hess_capasso_1987, title={New effects of structure in momentum and real space on nonlinear transport across heterojunction band discontinuities}, volume={51}, ISSN={0003-6951 1077-3118}, url={http://dx.doi.org/10.1063/1.98381}, DOI={10.1063/1.98381}, abstractNote={Nonlinear transport across heterojunction band discontinuities in strong electric fields is theoretically investigated. New phenomena which depend on the combined effects of the structure in real and momentum space are found. Reflections at the heterointerfaces, carrier overheating at the potential step, and the L→Γ, X→Γ backscattering bottlenecks produce pronounced peaks and anisotropies in the energy and momentum distributions, respectively. Finally, a new ionization rate overshoot effect due to the band structure difference between the two materials is discussed.}, number={7}, journal={Applied Physics Letters}, publisher={AIP Publishing}, author={Kim, Kiwook and Hess, Karl and Capasso, Federico}, year={1987}, month={Aug}, pages={508–510} }
 @article{kim_kahen_leburton_hess_1986, title={Band‐structure dependence of impact ionization rate in GaAs}, volume={59}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.337011}, DOI={10.1063/1.337011}, abstractNote={The band-structure dependence of the electron impact ionization rate in GaAs is studied by using local and nonlocal pseudopotential band structures and a Monte Carlo simulation code for the impact ionization rate α. We find that the difference in α for the two band structures reflects mainly the difference in the density of states.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kim, K. and Kahen, K. and Leburton, J. P. and Hess, K.}, year={1986}, month={Apr}, pages={2595–2596} }
 @article{kim_hess_1986, title={Simulations of electron impact ionization rate in GaAs in nonuniform electric fields}, volume={60}, ISSN={0021-8979 1089-7550}, url={http://dx.doi.org/10.1063/1.337135}, DOI={10.1063/1.337135}, abstractNote={A Monte Carlo simulation code has been developed to study the electron impact ionization in GaAs subject to nonuniform electric fields. Results are presented for the spatial evolution of the ionization rate and the average electron energy through a p+-n junction or Schottky barrier. We show that the dead space is significantly longer than estimated by simple ballistic models. For field variations typical for p+-n junctions or Schottky barriers, the results for the region after the dead space agree closely with steady-state calculations. Appropriate definition of the impact ionization rate in transient problems is discussed along with the Keldysh model.}, number={7}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Kim, K. and Hess, K.}, year={1986}, month={Oct}, pages={2626–2629} }