Structural and electrical characterization of AuTiAlTi/AlGaN/GaN ohmic contacts

AuTiAlTi/AlGaN/GaN ohmic contact structures rapid thermal annealed at 650, 750, 850, and 950 degreesC have been analyzed using complementary transmission electron microscopy and electrical characterization techniques. The relationship between annealing temperature, interfacial microstructure, and contact resistance is examined. Annealing temperatures of 750 degreesC or higher are required to produce an ohmic contact. Contacts annealed at 750 and 850 degreesC show a planar interface between contact and the AlGaN layer, with minimal consumption of the AlGaN and the formation of a thin TiN interfacial layer. Annealing at 950 degreesC produces the lowest contact resistance, with a structure showing inclusions through the AlGaN/GaN layer. These inclusions are also shown to be a Ti-nitride, having an Al/Au-rich metallurgical barrier layer surrounding them. However, this metallurgical layer does not produce an electrical barrier. (C) 2002 American Institute of Physics.