Low-resistance and transparent Ni-Co solid solution/Au ohmic contacts to p-type GaN for green GaN-based light-emitting diodes

We report on the formation of low-resistance and transparent p-type ohmic contact for green GaN-based light-emitting diodes (LEDs) using Ni-Co solid solution(5 nm)/Au(5 nm) scheme. The as-deposited Ni-Co solid solution(5 nm)/Au(5 nm) contact shows nonlinear current-voltage (I - V) characteristics. However, annealing the sample at 550 ^{{ring operator}}C in air results in the formation of ohmic contacts with specific contact resistance of 6.5×10^-4 Ω cm². The annealed sample shows light transmittance of 71.7% at a wavelength of 530 nm, which is better than that (64.9%) of oxidized Ni/Au contacts. Based on Auger electron spectroscopy and x-ray photoemission spectroscopy results, the annealing-induced improvement of the contacts is described and discussed.