Ohmic contacts to p-type Al _0.45Ga _0.55N

Ni, Pd, and Au Ohmic contacts to p-Al _0.45Ga _0.55N have been examined. We have observed that annealing the contacts in excess of 800°C is required to minimize the contact resistivity. However, the Pd and Au contacts annealed in excess of 700°C, which showed much better transport properties than Ni contacts annealed at the same temperatures, suffered from a rapid photoinduced degradation of both the current-voltage characteristics of the contacts and of the sheet resistance of the p-Al _0.45Ga _0.55N itself. This degradation was greatly reduced by passivating the p-Al _0.45Ga _0.55N surface with a SiN _x film. A hypothesis is presented to describe the observed degradation.