@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 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.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 is, hence, found to be unsuit...}, 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{haidet_sarkar_reddy_bryan_bryan_kirste_collazo_sitar_2017, title={Nonlinear analysis of vanadium- and titanium-based contacts to Al-rich n-AlGaN}, volume={56}, ISSN={["1347-4065"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85030640149&partnerID=MN8TOARS}, DOI={10.7567/jjap.56.100302}, abstractNote={In this work, we report on voltage dependent contact characteristics of Al-rich n-AlGaN due to the presence of a Schottky barrier at the metal–AlGaN interface. Current–voltage characteristics appear to be linear at low voltages, but a clear nonlinearity is evident at high voltages. Unlike Ga-rich n-AlGaN where V-based contact marginally outperforms the Ti-based contact, V-based contact to Al-rich n-AlGaN outperforms the Ti-based contact by ∼2 orders of magnitude for all voltage ranges. The improved performance of V-based contacts is likely due to a lower Schottky barrier and partly due to ease of formation of a low barrier V–AlGaN interface.}, number={10}, journal={JAPANESE JOURNAL OF APPLIED PHYSICS}, publisher={Japan Society of Applied Physics}, author={Haidet, Brian B. and Sarkar, Biplab and Reddy, Pramod and Bryan, Isaac and Bryan, Zachary and Kirste, Ronny and Collazo, Ramon and Sitar, Zlatko}, year={2017}, month={Oct} }
 @article{sarkar_haidet_reddy_kirste_collazo_sitar_2017, title={Performance improvement of ohmic contacts on Al-rich n-AlGaN grown on single crystal AlN substrate using reactive ion etching surface treatment}, volume={10}, ISSN={["1882-0786"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85021839341&partnerID=MN8TOARS}, DOI={10.7567/apex.10.071001}, abstractNote={Four orders of magnitude improvement in specific contact resistivity of Al-rich n-AlGaN grown on single crystal AlN substrates is achieved by surface treatment based on reactive ion etching (RIE). The ohmic contacts to as-grown Al-rich n-AlGaN/AlN exhibit a high contact resistance and nonlinearity due to a large Schottky barrier and low dislocation density. The RIE surface treatment reduces the barrier height at the free surface by ∼0.5 eV and is also expected to introduce a defective surface required for ohmic contact formation.}, number={7}, journal={APPLIED PHYSICS EXPRESS}, publisher={Japan Society of Applied Physics}, author={Sarkar, Biplab and Haidet, Brian B. and Reddy, Pramod and Kirste, Ronny and Collazo, Ramon and Sitar, Zlatko}, year={2017}, month={Jul} }
 @article{reddy_washiyama_kaess_breckenridge_hernandez-balderrama_haidet_alden_franke_sarkar_kohn_et al._2016, title={High temperature and low pressure chemical vapor deposition of silicon nitride on AlGaN: Band offsets and passivation studies}, volume={119}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/1.4945775}, DOI={10.1063/1.4945775}, abstractNote={In this work, we employed X-ray photoelectron spectroscopy to determine the band offsets and interface Fermi level at the heterojunction formed by stoichiometric silicon nitride deposited on AlxGa1-xN (of varying Al composition “x”) via low pressure chemical vapor deposition. Silicon nitride is found to form a type II staggered band alignment with AlGaN for all Al compositions (0 ≤ x ≤ 1) and present an electron barrier into AlGaN even at higher Al compositions, where Eg(AlGaN) > Eg(Si3N4). Further, no band bending is observed in AlGaN for x ≤ 0.6 and a reduced band bending (by ∼1 eV in comparison to that at free surface) is observed for x > 0.6. The Fermi level in silicon nitride is found to be at 3 eV with respect to its valence band, which is likely due to silicon (≡Si0/−1) dangling bonds. The presence of band bending for x > 0.6 is seen as a likely consequence of Fermi level alignment at Si3N4/AlGaN hetero-interface and not due to interface states. Photoelectron spectroscopy results are corroborated by current-voltage-temperature and capacitance-voltage measurements. A shift in the interface Fermi level (before band bending at equilibrium) from the conduction band in Si3N4/n-GaN to the valence band in Si3N4/p-GaN is observed, which strongly indicates a reduction in mid-gap interface states. Hence, stoichiometric silicon nitride is found to be a feasible passivation and dielectric insulation material for AlGaN at any composition.}, number={14}, journal={JOURNAL OF APPLIED PHYSICS}, publisher={AIP Publishing}, author={Reddy, Pramod and Washiyama, Shun and Kaess, Felix and Breckenridge, M. Hayden and Hernandez-Balderrama, Luis H. and Haidet, Brian B. and Alden, Dorian and Franke, Alexander and Sarkar, Biplab and Kohn, Erhard and et al.}, year={2016}, month={Apr} }
 @article{haidet_bryan_reddy_bryan_collazo_sitar_2015, title={A conduction model for contacts to Si-doped AlGaN grown on sapphire and single-crystalline AlN}, volume={117}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/1.4923062}, DOI={10.1063/1.4923062}, abstractNote={Ohmic contacts to AlGaN grown on sapphire substrates have been previously demonstrated for various compositions of AlGaN, but contacts to AlGaN grown on native AlN substrates are more difficult to obtain. In this paper, a model is developed that describes current flow through contacts to Si-doped AlGaN. This model treats the current through reverse-biased Schottky barriers as a consequence of two different tunneling-dependent conduction mechanisms in parallel, i.e., Fowler-Nordheim emission and defect-assisted Frenkel-Poole emission. At low bias, the defect-assisted tunneling dominates, but as the potential across the depletion region increases, tunneling begins to occur without the assistance of defects, and the Fowler-Nordheim emission becomes the dominant conduction mechanism. Transfer length method measurements and temperature-dependent current-voltage (I-V) measurements of Ti/Al-based contacts to Si-doped AlGaN grown on sapphire and AlN substrates support this model. Defect-assisted tunneling plays a much larger role in the contacts to AlGaN on sapphire, resulting in nearly linear I-V characteristics. In contrast, contacts to AlGaN on AlN show limited defect-assisted tunneling appear to be only semi-Ohmic.}, number={24}, journal={JOURNAL OF APPLIED PHYSICS}, publisher={AIP Publishing}, author={Haidet, Brian B. and Bryan, Isaac and Reddy, Pramod and Bryan, Zachary and Collazo, Ramon and Sitar, Zlatko}, year={2015}, month={Jun} }