Effects of sulfur passivation on Ti/Al ohmic contacts to n-type GaN using CH₃CSNH₂ solution

We investigate the effect of CH₃CSNH₂ solution treatment on Ti/Al ohmic contacts to n-GaN:Si (3×10¹⁸cm ^-3). It is shown that the sulfide treatment results in a drastic increase in the photoluminescence intensity, compared with that of the untreated sample. Current-voltage (I-V) results show that the sulfide treatment significantly improves the specific contact resistance. The annealing of the sulfide-treated sample (at 700°C) results in a specific contact resistance of 3.1×10^-6cm². X-ray photoemission spectroscopy (XPS) results show that the Ga 2p core levels shift toward the higher-binding energy side by 0.2 eV for the sulfide-treated sample and by 0.4 eV for the annealed (sulfide-treated) sample, compared with that of the untreated one. It is further shown that the intensity of O 1s core level decreases with the sulfide treatment. Based on the I-V and XPS results, the sulfide and annealing treatment dependence of the specific contact resistance is discussed.