ABSTRACT
Titanium (Ti) and palladium (Pd) barrier layers between the Al/Ti diffusion couple and the Silver (Au) capping layer of multilayer ohmic contacts to n-type AIGaN/GaN field effect transistors were found to be ineffective in preventing the diffusion of Au to the AIGaN following high temperature rapid thermal annealing. The formation of a band of Titanium nitride grains at the contact/AIGaN interface is responsible for the activation of the contact. Devices based on AIGaN/GaN heterostructures are of interest in the area of high power, high frequency applications. For such devices to become commercially viable, ohmic contacts must fulfil the requirements of reproducibility, low resistance and good thermal and mechanical stability. As AI and Ti layers are both susceptible to oxidation, Au is used as an oxidation resistant capping layer. The Au acts to assist with wire bonding. AuTiAITi contacts became ohmic at lower temperatures than the AuPdAITi contact containing similar amounts of Ti in the overall scheme.
