Nitrogen-vacancy-related defects and Fermi level pinning in n-GaN Schottky diodes

The relationship between the surface states related to nitrogen-vacancy defects and surface Fermi level pinning has been investigated using x-ray photoelectron spectroscopy and capacitance–voltage measurements. Barrier heights of 1.09, 0.50, 1.20, and 0.50 eV, 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 is very close to the Schottky limit, due to the reduction of the surface state density. This also suggests that a large number of surface states related to nitrogen-vacancy defects in the etched n-GaN surface would lead to the pinning of the Fermi level at 0.50 eV below the conduction band edge.