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Abstracts: The microstructure evolution of oxidized Ni (20nm)/Au (20nm) contact to p-GaN with increasing annealing temperature was studied by synchrotron X-ray diffraction (XRD) and powder XRD. With the increase of annealing temperature, it was observed that the Au on the p-GaN gradually grew on the p-GaN with the orientation relationship of Au(111)//GaN(0002). NiO also had such a orientation relationship of NiO(111)//GaN(0002) at 500°C and gradually turned back to polycrystalline structure at higher temperature. The orientation relationship of Au, NiO and GaN implied that the epitaxial crystallization might occur during annealing. The specific contact resistance also reduced to the minimum 2.73×10−4 Ωcm2 at 500°C. Therefore, plausibly the epitaxial crystallization is an important mechanism for lowering the contact resistance between oxidized Ni/Au contacts and p-GaN. [Copyright &y& Elsevier]