Nanoscale structural and electrical evolution of Ta- and Ti-based contacts on AlGaN/GaN heterostructures

In this paper, the nanoscale structural and electrical evolution of Ta- and Ti-based contacts was investigated employing several analytical techniques. A correlation between the improvement of the electrical quality of the contacts and the formation of Al-alloyed phases (TaAl3 or TiAl3) during annealing was observed. However, while for the Ti/Al contacts an Ohmic behavior with a contact resistance Rc=1.8Ohm.mm has been achieved after annealing at 500 °C, Ta/Al contacts exhibited a higher contact resistance (Rc=36.3Ohm.mm) even after annealing at 700 °C. The different electrical behaviour has been explained considering the different interface and the homogeneity of the current transport at a nanoscale level.