“…This metallic Ni layer shall be transformed into NiO, which is considered as a barrier to resist the diffusion of Ga atoms from Au when the samples were annealed in O 2 ambient. According to the literature [18], NiO/Au contacting on p-GaN can lead to the intermixing of both layers after annealing. Therefore, an additional Au layer was sputtered on Ni/Au layers to stabilize the contact from intermixing of Ni/Au layers.…”