Effect of Ga dissolution in Au of Ni–Au system on ohmic contact formation to p-type GaN

The effect of Ga dissolution in Au of Ni–Au system on ohmic contact formation to p-type GaN was carried out in this study. The Au (8 − x nm)/Ni (2 nm)/Au(x nm) deposited on p-GaN by magnetron sputtering system, where x = 0, 2, 4, and 6. It was discovered that after annealing in O2 ambient, the samples show ohmic characteristic when x is equal to 4 and 6. The TEM cross-sectional observation indicated that Ni did not diffuse to the GaN surface during annealing and the Ni transformed to NiO at the same time. The final microstructure became Au(8 − x)/NiO/Au(x)/p-GaN, where Au(8 − x) layer agglomerated into the semi-continuous and NiO was considered a barrier to prevent the diffusion of Ga atoms. Therefore, the presence of Au(x) plays a role to dissolve the Ga atoms from p-GaN, leaving Ga vacancies below the contact, thus increased the hole concentration of p-GaN. It is concluded that amount of Au(x) contacting to p-GaN is a key to achieve ohmic characteristics on p-GaN in this study.