Effects of surface treatments on the electrical and the microstructural changes of Pd contact an p-type GaN

We investigated the effects of surface treatments by aqua regia and (NH4)(2 )S-x on the electrical and the microstructural changes of Pd contact on p-t ype GaN during annealing. The formation of a surface oxide was suppressed b y the (NH4)(2)S-x treatment, and S-Ga and S-N bonds with binding energy of 162.1 eV and 163.6 eV were formed, degrading the structural ordering of Pd. After 300 degreesC annealing, the contact resistivity in the aqua regia-tr eated sample increased significantly. This could be attributed to the outdi ffusion of N atoms leaving N vacancies below the contact, as confirmed by t he increase of the Pd (111) plane spacing probably due to the dissolution o f N atoms in Pd interstitial sites. Meanwhile, the contact resistivity in t he (NH4)(2)S-x-treated sample was not degraded and no change was observed i n the Pd (111) plane spacing. These results suggest that S-Ga and S-N bonds formed on (NH4)(2)S-x-treated GaN could act as a diffusion barrier for the outdiffusion of N atoms. The contact resistivity for the aqua regia-treate d sample decreased again, probably due to the outdiffusion of Ga as well as N atoms at 500 degreesC.