Barrier height values of Ni contacts to (NH4)2Sx-treated p-type GaN (p-GaN) were obtained from current-voltage and x-ray photoelectron spectroscopy (XPS) measurements in this study. The induced deep level defect band through high Mg doping led to a reduction of the depletion layer width in the p-GaN near the interface and an increase in the probability of thermionic field emission (TFE). Furthermore, the calculated barrier height value of Ni contacts to (NH4)2Sx-treated p-GaN using the TFE model is close to the Schottky limit, which is in good agreement with the observed result by XPS measurements and suggests that (NH4)2Sx surface treatment leads to the removal of native oxides and the reduction of the surface state related to oxygen-induced and nitrogen-vacancy defects.
