Low-resistance and highly transparent Ni/indium-tin oxide ohmic contacts to phosphorous-doped p-type ZnO

The use of a Ni (50 Å)/indium tin oxide (ITO) (500 Å) bilayer scheme for low-resistance and transparent ohmic contacts to phosphorous doped p-type ZnO was investigated. Ni/indium tin oxide (ITO) (50/500 Å) layers were prepared by electron-beam evaporation. Although the as-deposited Ni/ITO contact was highly resistant and opaque, contact resistance and transparency were greatly improved by a thermal annealing process. A specific contact resistance as low as 6.2×10−5Ωcm2 was obtained after thermal annealing at 400 °C for 1 min under an N2 ambient. The measured light transmittance of the Ni/ITO (50/500 Å) bilayer on p-type ZnO was determined to be above 80% at a wavelength of 400–600 nm. These results strongly indicate that the use of a Ni/ITO has considerable promise for ZnO-based optical devices.