Ohmic contacts to p-type GaN based on TaN, TiN, and ZrN

Ohmic contacts to p-GaN using a Ni∕Au∕X∕Ti∕Au metallization scheme, where X is TaN, TiN, or ZrN, are reported. The dependence of the contact properties on annealing temperature (25–1000°C) in N2 is examined. For annealing temperatures greater than 500°C, the contacts display Ohmic characteristics and reach a minimum of about 2×10−4Ωcm2 after annealing at 700°C for 60s in a N2 ambient. The specific contact resistance is stable on annealing up to at least 1000°C. However, at high temperatures the morphology of the contacts are very rough and there is a large degree of intermixing between the metallic layers. The thermal stability of these contacts are superior as compared to conventional Ni∕Au, which display poor characteristics at annealing temperatures greater than 500°C.