Ohmic contact to nonpolar a-plane p-type GaN using Ni/Au

In this study, we examined the characteristics of Ni/Au (20 nm/80 nm) ohmic contacts to non-polar a-plane p-GaN as a function of annealing temperature. The current-voltage (I-V) curves were showed an upward curve with annealing when Ni/Au metals were used as ohmic metals to nonpolar p-GaN, which was similar to those of the other crystalline planes. The contact resistivity decreased from 2.36 to 6.95 × 10−3 Ω cm2. Secondary ion mass spectroscopy showed that the Ga atoms out-diffused from the GaN substrate after annealing at 400 °C, which led to the generation of Ga vacancies. The formation of Ga and N vacancies was found to be a competing process during annealing.