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 thi n and uniform Ni and Au layers, were investigated in situ using synchrotron photoemission spectroscopy. The study showed that the GaN surface layer wa s instantly disrupted as the result of Ni deposition, and the dissociated N and Ga were localized at the interface without the formation of any specif ic nitride species. The two Fermi levels of n- and p-type GaN were simultan eously located near 1.9 eV above the valence-band maximum, where the high-d ensity gap states were generated by Ni deposition. The uniform Au layer dep osited over the Ni layer tended to form an alloy with Ni as well as Ga atom s, but did not alter the band bending. A postannealing process enhanced tho se interfacial reactions, resulting in the segregation of Ga to the surface .