Influence of various annealing temperatures on microstructure evolution of oxidized Ni/Au ohmic contact to p-GaN studied by synchrotron X-ray diffraction

The influence of various annealing temperatures on microstructure evolution of oxidized Ni(20nm)/Au(20nm) ohmic contact to p-GaN was studied by synchrotron X-ray diffraction (XRD). In association with the variation of the specific contact resistance (ρc), it is observed that NiO and Au began to form partially epitaxial structure on p-GaN at 450°C, which played a critical role in lowering down the ρc. At 500°C, the epitaxial structure of Au and NiO was improved further while the lowest ρc was reached. However, at 600°C, the epitaxial structure of NiO was transformed to polycrystalline structure again with a sharp increase of ρc. Therefore, it is suggested that the degradation of the epitaxial structure of NiO is responsible for the sharp increase of ρc.