@article{reddy_washiyama_mecouch_hernandez-balderrama_kaess_breckenridge_sarkar_haidet_franke_kohn_et al._2018, title={Plasma enhanced chemical vapor deposition of SiO2 and SiNx on AlGaN: Band offsets and interface studies as a function of Al composition}, volume={36}, ISSN={["1520-8559"]}, DOI={10.1116/1.5050501}, abstractNote={In this work, the authors characterized the interface of plasma enhanced chemical vapor deposition (PECVD) dielectrics, SiO2 and SiNx with AlGaN as a function of Al composition. SiO2 is found to exhibit type I straddled band alignment with positive conduction and valence band offsets for all Al compositions. However, the interface Fermi level is found to be pinned within the bandgap, indicating a significant density of interface states. Hence, SiO2 is found to be suitable for insulating layers or electrical isolation on AlGaN with breakdown fields between 4.5 and 6.5 MV cm−1, but an additional passivating interlayer between SiO2 and AlGaN is necessary for passivation on Al-rich AlGaN. In contrast, Si-rich PECVD SiNx is found to exhibit type II staggered band alignment with positive conduction band offsets and negative valence band offsets for Al compositions <40% and type I straddled band alignment with negative conduction and valence band offsets for Al compositions >40% and is, hence, found to be unsuitable for insulating layers or electrical isolation on Al-rich AlGaN in general. In contrast to passivating stoichiometric LPCVD Si3N4, no evidence for interface state reduction by depositing SiNx on AlGaN is observed.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Reddy, Pramod and Washiyama, Shun and Mecouch, Will and Hernandez-Balderrama, Luis H. and Kaess, Felix and Breckenridge, M. Hayden and Sarkar, Biplab and Haidet, Brian B. and Franke, Alexander and Kohn, Erhard and et al.}, year={2018}, month={Nov} }
 @article{cai_mecouch_zheng_zhang_sitar_2008, title={Thermodynamic and kinetic study of transport and reaction phenomena in gallium nitride epitaxy growth}, volume={51}, ISSN={["0017-9310"]}, DOI={10.1016/j.ijheatmasstransfer.2007.12.004}, abstractNote={An iodine vapor phase epitaxy (IVPE) system has been designed and built to grow high quality thick gallium nitride film at the growth rate up to 80 μm/h with the deposition temperature of 1050 °C and the pressure of 200 torr. Numerical and experimental studies have been performed to investigate heat and mass transport and reaction phenomena in a vertical reactor. Geometrical parameters and operating conditions are optimized to achieve high and uniform GaN deposition rate. Gas phase and surface reactions in the growth chamber have been analyzed thermodynamically and kinetically, and primary transport species and important reactions are identified. The rate expressions for different surface reactions are determined and their contributions to the GaN deposition rate are studied for different V/III ratios. The sticking probability of the main reactants and adsorption activation energy are calculated.}, number={5-6}, journal={INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER}, author={Cai, D. and Mecouch, W. J. and Zheng, L. L. and Zhang, H. and Sitar, Z.}, year={2008}, month={Mar}, pages={1264–1280} }
 @article{mecouch_wagner_reitmeier_davis_pandarinath_rodriguez_nemanich_2005, title={Preparation and characterization of atomically clean, stoichlometric surfaces of AIN(0001)}, volume={23}, ISSN={["0734-2101"]}, DOI={10.1116/1.1830497}, abstractNote={In situ exposure of the (0001) surface of AlN thin films to flowing ammonia at 1120 °C and 10−4Torr removes oxygen∕hydroxide and hydrocarbon species below the detectable limits of x-ray photoelectron spectroscopy and decreases the Al∕N ratio from 1.3 to 1.0. The positions of the Al2p and the N1s core level peaks acquired from the cleaned surfaces were 75.0±0.1eV and 398.2±0.1eV, respectively, which were similar to the values determined for the as-loaded samples. The cleaning process left unchanged the (1×1) low energy electron diffraction pattern, the step-and-terrace microstructure, and the root mean square roughness values observed for the surfaces of the as-loaded samples; i.e., the surface structure and microstructure were not changed by the high-temperature exposure to ammonia at low pressures. Vacuum annealing under 10−7Torr at 1175 °C for 15 min removed all detectable hydrocarbons; however, it did not remove the oxygen∕hydroxide species.}, number={1}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Mecouch, WJ and Wagner, BP and Reitmeier, ZJ and Davis, RF and Pandarinath, C and Rodriguez, BJ and Nemanich, RJ}, year={2005}, pages={72–77} }
 @article{reitmeier_park_mecouch_davis_2004, title={In situ cleaning of GaN(0001) surfaces in a metalorganic vapor phase epitaxy environment}, volume={22}, number={5}, journal={Journal of Vacuum Science & Technology. A, Vacuum, Surfaces, and Films}, author={Reitmeier, Z. J. and Park, J. S. and Mecouch, W. J. and Davis, R. F.}, year={2004}, pages={2077–2082} }
 @article{cook_fulton_mecouch_davis_lucovsky_nemanich_2003, title={Band offset measurements of the GaN (0001)/HfO2 interface}, volume={94}, DOI={10.1063/1.1618374}, number={11}, journal={Journal of Applied Physics}, author={Cook, T. E. and Fulton, C. C. and Mecouch, W. J. and Davis, R. F. and Lucovsky, G. and Nemanich, R. J.}, year={2003}, pages={7155–7158} }
 @article{cook_fulton_mecouch_davis_lucovsky_nemanich_2003, title={Band offset measurements of the Si3N4/GaN (0001) interface}, volume={94}, ISSN={["0021-8979"]}, DOI={10.1063/1.1601314}, abstractNote={X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy were used to measure electronic states as Si3N4 was deposited on clean GaN (0001) surfaces. The n-type (2×1018) and p-type (1×1017) GaN surfaces were atomically cleaned in NH3 at 860 °C, and the n-and p-type surfaces showed upward band bending of ∼0.2±0.1 eV and downward band bending of 1.1±0.1 eV, respectively, both with an electron affinity of 3.1±0.1 eV. Layers of Si (∼0.2 nm) were deposited on the clean GaN and nitrided using an electron cyclotron resonance N2 plasma at 300 °C and subsequently annealed at 650 °C for densification into a Si3N4 film. Surface analysis was performed after each step in the process, and yielded a valence band offset of 0.5±0.1 eV. Both interfaces exhibited type II band alignment where the valence band maximum of GaN lies below that of the Si3N4 valence band. The conduction band offset was deduced to be 2.4±0.1 eV, and a change of the interface dipole of 1.1±0.1 eV was observed for Si3N4/GaN interface formation.}, number={6}, journal={JOURNAL OF APPLIED PHYSICS}, author={Cook, TE and Fulton, CC and Mecouch, WJ and Davis, RF and Lucovsky, G and Nemanich, RJ}, year={2003}, month={Sep}, pages={3949–3954} }
 @article{smith_mecouch_miraglia_roskowski_hartlieb_davis_2003, title={Evolution and growth of ZnO thin films on GaN(0001) epilayers via metalorganic vapor phase epitaxy}, volume={257}, ISSN={["1873-5002"]}, DOI={10.1016/S0022-0248(03)01469-6}, abstractNote={Zinc oxide thin films have been grown via metalorganic vapor phase epitaxy at 450°C and 250 Torr total pressure on O-terminated areas and micro-regions of native oxide formed on GaN(0 0 0 1) epilayers during exposure to the oxygen reactant. Analyses of the Ga3d core level spectra acquired from films grown for progressively longer times and comparisons of these data with both thermodynamic models of growth processes and associated atomic force micrographs revealed that the ZnO nucleated and grew via the Stranski–Krastanov mode. Considerations of (1) differences in surface energetics of the polar (0 0 0 1) surfaces of ZnO and GaN and that of the Ga-based oxide as well as (2) the relatively low stress generated by the moderate lattice mismatches in the a-axis lattice parameters of these compounds supported the observed growth mode. The shifts in the position of the Ga3d core level with increasing deposition time and decreasing peak intensity were caused by surface charging and increasing sampling volumes of the Ga-based oxide as well as the growing ZnO layer. The island/ocean morphology of the Ga-based oxide controlled the morphology of the initial ZnO layer, which, in turn controlled the locations and the morphologies of the subsequently nucleated ZnO islands. Scanning electron microscopy of thicker ZnO films revealed a highly textured microstructure.}, number={3-4}, journal={JOURNAL OF CRYSTAL GROWTH}, author={Smith, TP and Mecouch, WJ and Miraglia, PQ and Roskowski, AM and Hartlieb, PJ and Davis, RF}, year={2003}, month={Oct}, pages={255–262} }
 @article{cook_fulton_mecouch_tracy_davis_hurt_lucovsky_nemanich_2003, title={Measurement of the band offsets of SiO2 on clean n- and p-type GaN(0001)}, volume={93}, ISSN={["0021-8979"]}, DOI={10.1063/1.1559424}, abstractNote={The band alignment at the SiO2-GaN interface is important for passivation of high voltage devices and for gate insulator applications. X-ray photoelectron spectroscopy and ultraviolet photoemission spectroscopy have been used to observe the interface electronic states as SiO2 was deposited on clean GaN(0001) surfaces. The substrates, grown by metallorganic chemical vapor deposition, were n- (1×1017) and p-type (2×1018) GaN on 6H-SiC(0001) with an AlN(0001) buffer layer. The GaN surfaces were atomically cleaned via an 860 °C anneal in an NH3 atmosphere. For the clean surfaces, n-type GaN showed upward band bending of 0.3±0.1 eV, while p-type GaN showed downward band bending of 1.3±0.1 eV. The electron affinity for n- and p-type GaN was measured to be 2.9±0.1 and 3.2±0.1 eV, respectively. To avoid oxidizing the GaN, layers of Si were deposited on the clean GaN surface via ultrahigh vacuum e-beam deposition, and the Si was oxidized at 300 °C by a remote O2 plasma. The substrates were annealed at 650 °C for densification of the SiO2 films. Surface analysis techniques were performed after each step in the process, and yielded a valence band offset of 2.0±0.2 eV and a conduction band offset of 3.6±0.2 eV for the GaN-SiO2 interface for both p- and n-type samples. Interface dipoles of 1.8 and 1.5 eV were deduced for the GaN-SiO2 interface for the n- and p-type surfaces, respectively.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Cook, TE and Fulton, CC and Mecouch, WJ and Tracy, KM and Davis, RF and Hurt, EH and Lucovsky, G and Nemanich, RJ}, year={2003}, month={Apr}, pages={3995–4004} }
 @article{tracy_mecouch_davis_nemanich_2003, title={Preparation and characterization of atomically clean, stoichiometric surfaces of n- and p-type GaN(0001)}, volume={94}, ISSN={["1089-7550"]}, DOI={10.1063/1.1596369}, abstractNote={It is demonstrated that in situ exposure of the (0001) surface of n- and p-type GaN thin films to flowing ammonia at 860 °C and 10−4 Torr removes hydrocarbon and oxygen/hydroxide species below the detectable limits of x-ray and ultraviolet photoelectron spectroscopies (UPS) and decreases the Ga/N ratio from 1.3 to 1.0. Additional indications of the efficacy of this ammonia-based chemical vapor cleaning (CVC) process were the shifts in the Ga 3d and the N 1s core level positions from the as-loaded to the CVC surfaces of the n-type samples from 21.0±0.1 to 20.6±0.1 eV and from 398.3±0.1 to 398.0±0.1 eV, respectively, and the change in the UPS measured low energy spectrum turn on from 3.9±0.1 (as-loaded samples) to 3.0±0.1 eV (cleaned samples) below the Fermi level. Analogous changes in the p-type samples were from 19.6±0.1 to 18.9±0.1 eV and from 397.1±0.1 to 396.3±0.1 eV for the Ga 3d and the N 1s core levels, and from 3.0±0.1 to 1.1±0.1 eV for the UPS valence band maximum (VBM). The VBM values of the CVC samples indicate band bending of ∼0.3 eV upward on n type and ∼0.8 eV downward on p type. Electron affinities of 2.8±0.1 and 2.6±0.1 eV were determined for the clean n-type and p-type surfaces, respectively. Irrespective of doping, the CVC process left unchanged the (1×1) low energy diffraction pattern, the terraced microstructure, and the root mean square roughness observed for the surfaces of the as-loaded samples, i.e., the surface microstructure was not damaged during the high temperature exposure to ammonia at low pressure.}, number={5}, journal={JOURNAL OF APPLIED PHYSICS}, author={Tracy, KM and Mecouch, WJ and Davis, RF and Nemanich, RJ}, year={2003}, month={Sep}, pages={3163–3172} }