The relationship between the surface states related to N-vacancy defects and surface Fermi level pinning was investigated by using X-ray photoelectron spectroscopy and capacitance–voltage measurements. Barrier heights of 1.09, 0.50, 1.20 and 0.50eV, respectively, were obtained for Ni/(NH4)2Sx-treated n-GaN, Ni/etched n-GaN, Au/(NH4)2Sx-treated n-GaN and Au/etched n-GaN Schottky diodes. For Schottky diodes treated with (NH4)2Sx, the observed Schottky barrier height was very close to the Schottky limit, due to the reduction of the surface state density. This also suggested that a large number of surface states related to N-vacancy defects in the etched n-GaN surface would lead to the pinning of the Fermi level at 0.50eV below the conduction band edge.

Nitrogen-Vacancy Related Defects and Fermi Level Pinning in n-GaN Schottky Diodes. Y.J.Lin, Q.Ker, C.Y.Ho, H.C.Chang, F.T.Chien: Journal of Applied Physics, 2003, 94[3], 1819-22