Effects of Surface Treatments on the Electrical and the Microstructural Changes of Pd Contact on p-type GaN

摘要

We investigated the effects of surface treatments by aqua regia and (NH_4)_2Sx on the electrical and the microstructural changes of Pd contact on p-type GaN during annealing. The formation of a surface oxide was suppressed by the (NH_4)_2Sx treatment, and S-Ga and S-N bonds with binding energy of 162.1 eV and 163.6 e V were formed, degrading the structural ordering ofPd. After 300degC annealing, the contact resistivity in the aqua regia-treated sample increased significantly. This could be attributed to the outdiffusion of N atoms leaving N vacancies below the contact, as confIrmed by the increase of the Pd (111) plane spacing probably due to the dissolution of N atoms in Pd interstitial sites. Meanwhile, the contact resistivity in the (NH_4)_2Sx-treated sample was not degraded and no change was observed in the Pd (111) plane spacing. These results suggest that S-Ga and S-N bonds formed on (NH_4)_2Sx-treated GaN could act as a diffusion barrier for the outdiffusion of N atoms. The contact resistivity for the aqua regia-treated sample decreased again, probably due to the outdif- fusion of Ga as well as N atoms at 500degC.