Low-resistivity and transparent indium-oxide-doped ZnO ohmic contact to p-type GaN

We report on the indium-oxide-doped ZnO (IZO) transparent ohmic contact to the p-GaN. The IZO transparent ohmic contact layer was deposited on p-GaN by e-beam evaporation. The transmittance of an IZO film with a thickness of 250nm was 84%–92% for the light in the wavelength range of 400 and 600nm. In addition, the IZO contact film yielded a low specific contact resistance of 3.4×10−4Ωcm2 on p-GaN when annealed at 600°C for 5min under a nitrogen ambient. Auger electron spectroscopy and x-ray photoemission spectroscopy analyses of the IZO and p-GaN interface indicated that Ga atoms had out-diffused and an InN phase was formed at the interface region after the thermal annealing process, resulting in a decrease in contact resistance. The light output power of a light-emitting diode (LED) with an IZO ohmic contact layer was increased by 34% at 83mW of electrical input power compared to that of a LED with a Ni∕Au ohmic contact layer.