Effects of annealing in an oxygen ambient on electrical properties of ohmic contacts to p-type GaN

Effects of annealing ambient of an oxygen and nitrogen mixed gas on the electrical properties were studied for Au-based ohmic contacts (NiAu, CoAu, CuAu, PdAu, and PtAu) to p-type GaN. Addition of oxygen to the nitrogen gas reduced the specific contact resistances (rho(c)) and resitivities of the p-GaN epilayers (rho(s)) of the contacts after annealing at temperatures of 500 similar to 600 degrees C. The microstructural analysis at the p-GaN/metal interfaces did not detect the heterostructural intermediate semiconductor layer at the GaN/metal interfaces. The reason for reduction of both the rho(c) and rho(s) values by the oxygen gas addition was believed to be due to formation of the p-GaN epilayer with high hole concentrations, caused by removal of hydrogen atoms which bonded with Mg atoms.