Low-resistance and high-transparency Ni/indium tin oxide ohmic contacts to p-type GaN

Abstract

The characteristics of Ni/indium tin oxide (ITO) ohmic contacts to p-type GaN ${\text{(∼2×10}}^{17} {\mathrm{cm}}^{\mathrm{-3}})$ have been studied. The Ni/ITO (10 nm/250 nm) layers were prepared by thermal evaporation and rf magnetron sputtering, respectively. Although the as-deposited Ni/ITO contacts present rectified behavior, the linear current–voltage characteristics can be obtained. The contact resistance can be reduced significantly for the $\mathrm{ITO/Ni}\mathrm{/p-}\mathrm{GaN}$ samples after suitable rapid thermal process. The contact property of $\mathrm{ITO/Ni}\mathrm{/p-}\mathrm{GaN}$ shows lowest specific contact resistivity of ${\text{8.6×10}}^{\text{−4}}\mathrm{ \Omega }{\mathrm{cm}}^{\mathrm{2}}$ and high transparency (above 80% for 450–550 nm) as the sample annealed at 600 °C in air. Possible mechanisms for the observed low contact resistance and high transparency will be discussed. The present process is compatible with the fabrication for the high-efficient GaN light-emitting devices.