Effect of alcohol-based sulfur treatment on Pt Ohmic contacts to p-type GaN

The effects of an alcohol-based (NH4)(2)S solution [t-C4H9OH+(NH4)(2)S] treatment on Pt Ohmic contacts to p-type GaN are presented. The specific contact resistance decreased by three orders of magnitude from 2.56x10(-2) to 4.71x10(-5) Omega cm(2) as a result of surface treatment using an alcohol-based (NH4)(2)S solution compared to that of the untreated sample. The O 1s and Pt 4f core-level peaks in the x-ray photoemission spectra showed that the alcohol-based (NH4)(2)S treatment was effective in removing of the surface oxide layer. Compared to the untreated sample, the alcohol-based (NH4)(2)S-treated sample showed a Ga 2p core-level peak which was shifted toward the valence-band edge by 0.25 eV, indicating that the surface Fermi level was shifted toward the valence-band edge. These results suggest that the surface barrier height for hole injection from Pt metal to p-type GaN can be lowered by the surface treatment, thus resulting in a drastic reduction in specific contact resistance. (C) 2001 American Institute of Physics.