Highly reflective Ag/La bilayer ohmic contacts to p-type GaN

A new Ag/La bilayer metal contact scheme has been developed for producing high reflectance and low contact resistivity ohmic contacts to p-GaN. An excellent reflectance of over 91% at 460 nm wavelength and low specific contact resistivity of 1.6× 10^-4 ω cm² were obtained from Ag/La (150/20 nm) contact annealed at 450°C for 1 min. The La overlayer was oxidized to form La₂ O₃ when exposed to air, which effectively suppresses exposure of the Ag layer to oxygen atmosphere during annealing, leading to a good ohmic contact with smooth surface morphology and high reflectance. Additionally, Ag/La contacts show excellent thermal stability after a long thermal annealing at 300°C in air ambient.