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

Abstract

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 ∘C in air results in the formation of ohmic contacts with specific contact resistance of 6.5×10 −4 Ω cm 2. 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.