Abstract: Three different solutions ［dilute HCl,(NH4)2S,and aqua regia］ are used to treat a p-GaN surface,and bi-layer Ni/Au films are used as ohmic contacts to p-GaN.XPS spectra show that the (NH4)2S and aqua regia are more effective in removing the native oxide of the p-GaN than the dilute HCl.By comparing and analyzing I-V characteristics,the specific contact resistances,and the relative Ga/N atomic concentration ratio on p-type GaN surfaces of these samples,we concluded that there are more Ga vacancies in the aqua regia treated p-GaN surface and a higher ohmic contact performance can be obtained.

Key words: GaN, ohmic contact, CTLM