@article{park_ozbek_ma_veety_morgensen_barlage_wheeler_johnson_2010, title={An analytical model of source injection for N-type enhancement mode GaN-based Schottky Source/Drain MOSFET's with experimental demonstration}, volume={54}, ISSN={["0038-1101"]}, DOI={10.1016/j.sse.2010.06.013}, abstractNote={Abstract This study investigates the effect of the Gate-to-Source/Drain overlap structure of a GaN Schottky Source/Drain MOSFET. The Gate-to-Source overlap structure of the device allows the gate electric field to reduce the height of the Nickel(source)–GaN Schottky barrier near the SiO 2 –GaN interface at the source side, injecting more thermionically generated carriers over the partially reduced Schottky barrier. Based on this Schottky barrier lowering mechanism, an analytical model was developed. The analytical model shows that the reduction of the Schottky barrier height by 0.25 eV increases the on-state drain current by two orders of magnitude, which is in agreement of the previously reported TCAD simulation result in [6] . A specifically designed GaN Schottky Source/Drain MOSFET with the Gate-to-Source/Drain overlap structure was fabricated and characterized; the I D – V DS characteristic of the device shows that the on-state drain current of the device was increased by up to 160× compared to the same kind of device without the overlap structure (reported in Lei Ma (2007) [7] ), which is in agreement with the analytical model described herein.}, number={12}, journal={SOLID-STATE ELECTRONICS}, author={Park, Jaehoon and Ozbek, Ayse M. and Ma, Lei and Veety, Matthew T. and Morgensen, Michael P. and Barlage, Douglas W. and Wheeler, Virginia D. and Johnson, Mark A. L.}, year={2010}, month={Dec}, pages={1680–1685} }
 @article{grenko_ebert_reynolds_duscher_barlage_johnson_preble_paskova_evans_2010, title={Optimization of homoepitaxially grown AlGaN/GaN heterostructures}, volume={207}, ISSN={["1862-6300"]}, DOI={10.1002/pssa.200925508}, abstractNote={AbstractWe report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi‐insulating c‐axis GaN substrates by metalorganic vapor phase epitaxy (MOVPE). A room temperature (RT) Hall mobility (µRT) up to 2065 cm2 V−1 s−1 at sheet density (ns) of 8.25 × 1012 cm−2 has been measured. This work compliments prior studies in which we observed a buffer‐induced modulation of the RT two‐dimensional electron gas (2DEG) ns and µRT by varying the GaN buffer layer thickness. Here, we focus on the optimization of the heterostructure 2DEG properties by elimination of silicon doping in the Al0.25Ga0.75N barrier and unintentional Al in the not‐intentionally doped (n.i.d.) GaN buffer layer. The 15% improvement in µRT and ns relative to previous results is consistent with those predicted by Poisson solver calculations. Use of thick GaN buffers has minimized the theoretical mobility reduction based on intersubband scattering and has enabled us to determine the 2DEG sheet density associated with the polarization field ($n_{{\rm s}}^{{\rm polar}} $) to be ∼5 × 1012 cm−2.}, number={10}, journal={PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE}, author={Grenko, J. A. and Ebert, C. W. and Reynolds, C. L., Jr. and Duscher, G. J. and Barlage, D. W. and Johnson, M. A. L. and Preble, E. A. and Paskova, T. and Evans, K. R.}, year={2010}, month={Oct}, pages={2292–2299} }
 @article{lai_paskova_wheeler_grenko_johnson_barlage_udwary_preble_evans_2009, title={Excitation current dependent cathodoluminescence study of InGaN/GaN quantum wells grown on m-plane and c-plane GaN substrates}, volume={106}, ISSN={["1089-7550"]}, DOI={10.1063/1.3264729}, abstractNote={InGaN/GaN quantum wells (QWs) grown with identical conditions on m-plane and c-plane GaN substrates were studied by cathodoluminescence spectroscopy. At a low current of 10 nA, the emission intensity and wavelength of the m-plane aligned QWs were found to be about two times stronger and 19.5 nm blueshifted with respect to that of the c-plane aligned QWs. An increase in the current over three orders of magnitude was found to result in an increase in the emission intensities, with faster saturation in the m-plane aligned QWs. This was explained by the screening of quantum-confined Stark effect in the emission efficiency of the c-plane aligned QWs.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Lai, K. Y. and Paskova, T. and Wheeler, V. D. and Grenko, J. A. and Johnson, M. A. L. and Barlage, D. W. and Udwary, K. and Preble, E. A. and Evans, K. R.}, year={2009}, month={Dec} }
 @misc{jin_zeng_ma_barlage_2007, title={Analytical threshold voltage model with TCAD simulation verification for design and evaluation of tri-gate MOSFETs}, volume={51}, ISSN={["0038-1101"]}, DOI={10.1016/j.sse.2007.01.023}, abstractNote={The dynamics of the threshold voltage calculation is evaluated for the tri-gate architecture of device. The 3-D poisson's equation with eight boundary conditions is solved analytically and an analytical threshold model for tri-gate Si MOSFET device is developed. TCAD simulation result of the same device structure is also presented and it agrees well with our threshold analytical model. Furthermore, this analytical threshold model is capable of doing rudimentary first order comparisons of the threshold voltage with respect to device dimensions and semiconductor material type.}, number={3}, journal={SOLID-STATE ELECTRONICS}, author={Jin, Yawei and Zeng, Chang and Ma, Lei and Barlage, Doug}, year={2007}, month={Mar}, pages={347–353} }
 @article{adekore_davis_barlage_2007, title={Electrical and optical properties of ZnO (000(1)over-bar) wafers implanted with argon}, volume={101}, number={2}, journal={Journal of Applied Physics}, author={Adekore, B. T. and Davis, R. F. and Barlage, D. W.}, year={2007} }
 @article{adekore_pierce_davisb_barlage_muth_2007, title={Nitrogen acceptors in bulk ZnO (000(1)over-bar)) substrates and homoepitaxial ZnO films}, volume={102}, ISSN={["1089-7550"]}, DOI={10.1063/1.2751097}, abstractNote={Bulk single crystals of unintentionally doped ZnO having charge carrier concentration, ND−NA values of ∼1017 cm−3 were implanted with N+ ions at dosages of 1015 and 1016 cm−2 at 95 keV to a depth of 150 nm. The resulting p−n structure having acceptor concentrations ranging from 1017 to 1018 cm−3 was compared with nitrogen doped homoepitaxial films with ∼8×1017 cm−3 acceptors. Photoluminescence spectra acquired at 8 K showed an increase in the peak for the neutral donor-bound to acceptor-bound transition at 3.210 eV with increasing annealing temperature, thermal activation of a unique donor to acceptor transition due to nitrogen at 3.067 and 3.057 eV for implanted and epitaxial films, respectively; and an increase in the intensity of the defect-related green band at selected temperatures. Electroluminescence measurements at 300 K revealed an ultraviolet band, direct band-to-band recombination at 3.34 eV, donor-acceptor pair recombinations at 3.19 and 3.0 eV, and recombination in the green region centered at 2.49 eV. Current-voltage characteristics of implanted and homoepitaxial p−n diodes were also determined.}, number={2}, journal={JOURNAL OF APPLIED PHYSICS}, author={Adekore, B. T. and Pierce, J. M. and Davisb, R. F. and Barlage, D. W. and Muth, J. F.}, year={2007}, month={Jul} }
 @article{saripalli_pei_biggerstaff_ramachandran_duscher_johnson_zeng_dandu_jin_barlage_2007, title={Transmission electron microscopy studies of regrown GaN Ohmic contacts on patterned substrates for metal oxide semiconductor field effect transistor applications}, volume={90}, ISSN={["1077-3118"]}, DOI={10.1063/1.2741123}, abstractNote={Contact selected area regrowth of GaN was performed by metal organic chemical vapor deposition using a silicon nitride dielectric hard mask to define plasma etched recesses and to define source-drain regions. A low temperature regrowth process at 750–850°C was adopted to limit lateral overgrowth. High resolution electron microscopy images and selected area diffraction confirmed the regrowth selectivity and revealed that the low temperature regrown GaN is epitaxial and has a wurtzite crystal structure. I-V characteristics of the fabricated metal oxidesemiconductor field effect transistor show enhancement mode operation.}, number={20}, journal={APPLIED PHYSICS LETTERS}, author={Saripalli, Y. N. and Pei, L. and Biggerstaff, T. and Ramachandran, S. and Duscher, G. J. and Johnson, M. A. L. and Zeng, C. and Dandu, K. and Jin, Y. and Barlage, D. W.}, year={2007}, month={May} }
 @article{wang_park_saripalli_johnson_zeng_barlage_long_2006, title={Optical spectroscopic analysis of selected area epitaxially regrown n(+) gallium nitride}, volume={99}, ISSN={["1089-7550"]}, DOI={10.1063/1.2204755}, abstractNote={Gallium nitride (GaN) metal-insulator-semiconductor field-effect transistor with regrown by selected area metal organic vapor-phase-epitaxy n+ layer has been analyzed by micro-Raman and microphotoluminescence (micro-PL) spectroscopy. The material properties of the regrown n+ layer and the intrinsic layer in the gate region were extracted by using both spectroscopies. The free-carrier concentration of the regrown GaN layer and the intrinsic layer were determined by line shape analysis of the coupled plasmon-phonon mode to be 4.7×1017 and <3×1016cm−3, respectively. The inefficient substitutions of Ga vacancy (VGa) by Si result in relatively low carrier concentration in the regrown GaN layer. From the shift of E2(2) Raman peak and the near-band-edge (NBE) PL peak, the biaxial compressive stress in the intrinsic layer was found to be 0.4GPa. The residual stress was found to be fully relaxed in the regrown layer. The Si doping concentration in the regrown layer was determined to be 2×1019cm−3 based on the potential fluctuations introduced redshift of its NBE PL peak.}, number={12}, journal={JOURNAL OF APPLIED PHYSICS}, author={Wang, D. and Park, M. and Saripalli, Y. N. and Johnson, M. A. L. and Zeng, C. and Barlage, D. W. and Long, J. P.}, year={2006}, month={Jun} }
 @article{dandu_saripalli_braddock_johnson_barlage_2005, title={Characterization and modeling of AlGaN/GaN MOS capacitor with leakage for large signal transistor modeling}, volume={15}, ISSN={["1531-1309"]}, DOI={10.1109/LMWC.2005.856680}, abstractNote={Dual mode AlGaN/GaN metal oxide semiconductor (MOS) heterostructure field-effect transistor (HFET) devices were fabricated and characterized. In HFET mode of operation the devices showed an f/sub t//spl middot/L/sub g/ product of 12GHz/spl middot//spl mu/m at Vgs=-2 V. The AlGaN devices showed formation of an accumulation layer under the gate in forward bias and a f/sub t//spl middot/L/sub g/ product of 6GHz/spl middot//spl mu/m was measured at Vgs=5 V. A novel piecewise small signal model for the gate capacitance of MOS HFET devices is presented and procedures to extract the capacitance in presence of gate leakage are outlined. The model accurately fits measured data from 45MHz to 10GHz over the entire bias range of operation of the device.}, number={10}, journal={IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS}, author={Dandu, K and Saripalli, Y and Braddock, D and Johnson, M and Barlage, DW}, year={2005}, month={Oct}, pages={664–666} }
 @article{sonkusale_amsinck_nackashi_di spigna_barlage_johnson_franzon_2005, title={Fabrication of wafer scale, aligned sub-25 nm nanowire and nanowire templates using planar edge defined alternate layer process}, volume={28}, ISSN={["1873-1759"]}, DOI={10.1016/j.physe.2005.01.010}, abstractNote={We have demonstrated a new planar edge defined alternate layer (PEDAL) process to make sub-25 nm nanowires across the whole wafer. The PEDAL process is useful in the fabrication of metal nanowires directly onto the wafer by shadow metallization and has the ability to fabricate sub-10 nm nanowires with 20 nm pitch. The process can also be used to make templates for the nano-imprinting with which the crossbar structures can be fabricated. The process involves defining the edge by etching a trench patterned by conventional i-line lithography, followed by deposition of alternating layers of silicon nitride and crystallized a-Si. The thickness of these layers determines the width and spacing of the nanowires. Later the stack is planarized to the edge of the trench by spinning polymer Shipley 1813 and then dry etching the polymer, nitride and polysilicon stack with non-selective RIE etch recipe. Selective wet etch of either nitride or polysilicon gives us the array of an aligned nanowires template. After shadow metallization of the required metal, we get metal nanowires on the wafer. The process has the flexibility of routing the nanowires around the logic and memory modules all across the wafer. The fabrication facilities required for the process are readily available and this process provides the great alternative to existing slow and/or costly nanowire patterning techniques.}, number={2}, journal={PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES}, author={Sonkusale, SR and Amsinck, CJ and Nackashi, DP and Di Spigna, NH and Barlage, D and Johnson, M and Franzon, PD}, year={2005}, month={Jul}, pages={107–114} }
 @article{saripalli_zeng_long_barlage_johnson_braddock_2006, title={Properties of III-N MOS structures with low-temperature epitaxially regrown ohmic contacts}, volume={287}, ISSN={["1873-5002"]}, DOI={10.1016/j.jcrysgro.2005.10.075}, abstractNote={A significant limitation in the fabrication of III-N MOSFET relates to the formation of ohmic contacts for enhancement-mode MOSFET structures. Unlike existing III-N HFET devices, which include a high free-carrier density two-dimensional electron gas (2DEG) in the semiconductor substrate, a MOSFET in either accumulation or inversion mode require low free-carrier concentrations for the semiconductor channel to have an off-state. The applied gate bias enhances the free-carrier density in the channel, turning on the FET. Unfortunately, a low free-carrier density substrate is problematic for the formation of ohmic contacts, a problem usually dealt with in silicon MOS through self-aligned ion implantation. The high annealing temperatures associated with activating implanted dopants to substitutional sites limits the use of ion implantation for III-N MOSFET fabrication. To overcome this difficulties, selected area epitaxial re-growth of doped III-N materials was developed to form source-drain contacts on otherwise low-doped III-N epitaxial substrates, yielding the needed N+/n−/N+ or N+/p−/N+ structures. Contact re-growth was performed by MOVPE using a silicon nitride dielectric mask defining plasma-etched recesses in the source-drain region. A significant acceleration in the growth rate and surface roughening was observed following re-growth relative to a non-selective area epitaxial growth due to the reduced fill-factor, motivating a general change in MOVPE-operating conditions during re-growth. As the re-growth was intentionally designed to limit the lateral extent of the source-drain regions, the MOVPE re-growth process was performed under conditions limiting lateral overgrowth. III-N MOSFET structures with epitaxial regrown contacts are projected to provide a pathway for low threshold voltage devices suitable for amplifier or logic applications.}, number={2}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Saripalli, YN and Zeng, C and Long, JP and Barlage, DW and Johnson, MAL and Braddock, D}, year={2006}, month={Jan}, pages={562–565} }