Low resistance and transparent Ni-La solid solution/Au ohmic contacts to p-type GaN

A sodium (Ni)-Lanthanum (La) solid solution (ss) (8 nm)/Au (8 nm) ohmic contact schemes used for the formation of high-quality ohmic contacts to p-GaN were investigated. The formation of the ohmic contacts to p-GaN were investigated using Auger electron spectroscopy and X-ray photoemission spectroscopy. When contacts were annealed at temperature of 350°C-550°C for 1 min in air ambient, an improved current-voltage characteristics was observed. Results show that the temperature dependence of the ohmic properties of the NiLa ss/Au contacts is due to the combined effects of the shift of the surface Fermi level toward the valence-band edge and the formation of conductive oxide.