Electronic structure of oxidized Ni/Au contacts on p-GaN investigated by x-ray absorption spectroscopy

X-ray absorption spectroscopy has been used to investigate the electronic s tructure of as-deposited and oxidized Ni/Au contacts on p-GaN. The Ni K-, L -2,L-3-, and O K-edges x-ray absorption spectra clearly show the formation of NiO in the annealed contacts. Annealing in air increases Ni-site hole co ncentration and slightly shortens the nearest-neighbor Ni-O bond length, wh ich enhances p-d hybridization and charge transfer from Ni to O. The observ ed very low specific contact resistance in the oxidized contacts is found t o be due to the enhanced hole concentration at the Ni site. (C) 2001 Americ an Institute of Physics.