@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{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{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{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{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{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{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{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{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{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{littlejohn_hauser_glisson_1977, title={VELOCITY-FIELD CHARACTERISTICS OF GAAS WITH GAMMA-6(C)-L6(C)-X6(C) CONDUCTION-BAND ORDERING}, volume={48}, ISSN={["0021-8979"]}, DOI={10.1063/1.323516}, abstractNote={This paper describes Monte Carlo calculations of velocity-field characteristics for GaAs using the recent experimental conduction-band ordering of Aspnes, which places the Lc6(111) conduction-band minima lower in energy than the Xc6(100) minima. These calculations use intervalley deformation potentials which give the best fit to recent high-field drift velocity measurements, and at the same time give good agreement with accepted peak velocity and threshold field values.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={LITTLEJOHN, MA and HAUSER, JR and GLISSON, TH}, year={1977}, pages={4587–4590} }