Interfacial reaction and Fermi level movement induced by sequentially deposited metals on GaN: Au/Ni/GaN

The interfacial reaction and Fermi-level movement, which are induced by thin and uniform Ni and Au layers, were investigated in situ using synchrotron photoemission spectroscopy. The study showed that the GaN surface layer was instantly disrupted as the result of Ni deposition, and the dissociated N and Ga were localized at the interface without the formation of any specific nitride species. The two Fermi levels of n- and p-type GaN were simultaneously located near 1.9 eV above the valence-band maximum, where the high-density gap states were generated by Ni deposition. The uniform Au layer deposited over the Ni layer tended to form an alloy with Ni as well as Ga atoms, but did not alter the band bending. A postannealing process enhanced those interfacial reactions, resulting in the segregation of Ga to the surface.