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Ohmic contact formation to bulk and heterostructure gallium nitride family semiconductors

Rahman, F. and Xu, S. and Watson, I.M. and Mutha, D.K.B. and Oxland, R.K. and Johnson, N.P. and Bannerjee, A. and Wasige, E. (2009) Ohmic contact formation to bulk and heterostructure gallium nitride family semiconductors. Applied Physics A: Materials Science and Processing, 94 (3). pp. 633-639. ISSN 0947-8396

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We describe experiments investigating the quality of ohmic contacts to both bulk GaN and to III-nitride heterostructures. Titanium-based contacts were investigated to assess the role of intermixing and surface impurities for contact formation to n-type GaN. Direct contact to the two-dimensional electron gas in GaN/AlGaN heterostructures was also studied. These contacts were made by photochemical etching of the samples to expose the heterointerface. It was observed that even in the latter case contact annealing leads to a lower contact resistance by consuming surface contaminants and promoting beneficial interfacial reactions. Various passivation techniques were tried to reduce surface leakage current between contact pads and PECVD-deposited silicon nitride was found to be the best material for this application.