Electrical and Microstructural Characteristics of Ohmic Contacts formation on AlGaN/GaN HEMT

Electrical and microstructural characterization of Ti/Al/Ti/Au ohmic contact scheme for AlGaN/GaN heterostructures is presented. It has been found that the Al/Ti thickness ratio influences the Ga-Au phase formation, which is linked to the contact resistivity, and that an Al excess content leads to a rough surface. The thickness of the barrier layer (Ti) was found to play an important role to achieve simultaneously low ohmic contact resistance and good line edge definition, although it does not act as an effective diffusion barrier. The role of the thermal annealing cycles is also discussed.