Highly reflective low resistance Ag-based Ohmic contacts on p-type GaN using Mg overlayer

A metallization scheme with high reflectance and smooth surface morphology has been developed for obtaining low resistance Ohmic contacts on p-type GaN. Excellent Ohmic characteristics with a specific contact resistivity as low as 9.0×10−6Ωcm2 were obtained by annealing evaporated Ni (10Å)∕Ag (1500Å)∕Mg (500Å) contact at 450°C for 2min in O2 ambient. Additionally, a high reflectance over 80% was observed in the 400–500nm wavelength range. The Mg overlayer suppressed excessive incorporation of oxygen into the Ni and Ag layers during oxidation annealing, leading to high reflectance and smooth surface quality of the Ohmic contact.