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

The characteristics of Ni/indium tin oxide (ITO) ohmic contacts to p-type GaN (∼2×10¹⁷ cm^-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 ITO/Ni/p-GaN samples after suitable rapid thermal process. The contact property of ITO/Ni/p-GaN shows lowest specific contact resistivity of 8.6× 10^-4 Ω cm² 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.