Effects of surface treatment on Fermi level pinning at metal/GaN interfaces formed on homoepitaxial GaN layers

The effect of chemical surface treatment on the uncontrolled surface oxide at a GaN surface and on Fermi level pinning at subsequently formed metal/GaN interfaces was investigated for a GaN epitaxial layer grown on a GaN substrate. The impact of several chemical treatments, including photolithography, on the surface oxide and the resultant surface band bending at the GaN surface was examined by X-ray photoelectron spectroscopy. Surface band bending was reduced by the reduction in the amount of uncontrolled surface oxide. The metal/GaN interfaces formed subsequent to these chemical treatments were investigated by electrical measurement for Schottky barrier diodes. We found that the reduction in the amount of uncontrolled surface oxide leads to an increase in the slope factor in the metal-work-function dependence of the Schottky barrier height. The mechanism of Fermi level pinning at the metal/GaN interface is discussed.