TEM Assessment of AuTiAlTi and AuPdAlTi Ohmic Contacts to AlGaN/GaN

Abstract

AuTiAlTi and AuPdAlTi contacts to AlGaN/GaN, rapid thermal annealed at temperatures ranging from 650 to 950 °C have been investigated using conventional and chemical TEM analysis. Ohmic behaviour was seen for AuTiAlTi contacts annealed at 750 °C or higher and in AuPdAlTi contacts annealed at 850 °C or higher. The formation of interfacial TiN after anneals at high temperatures is required to activate the contact. At anneals of 950 °C, the samples show a structure of TiN grains within an interfacial band, with TiN inclusions into the AlGaN preceded by an Al–Au diffusion front. The presence of these inclusions does not appear to have any effect on the resistivity of the contact. Neither Ti nor Pd diffusion barriers have prevented the interdiffusion of Au through the Al and Ti contact layers. The implication is that the presence of Au mediates the formation of TiN at the annealing temperatures used in these samples.