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 250 nm was 84%-92% for the light in the wavelength range of 400 and 600 nm. In addition, the IZO contact film yielded a low specific contact resistance of 3.4× 10-4 Ω cm2 on p-GaN when annealed at 600 °C for 5 min 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 83 mW of electrical input power compared to that of a LED with a NiAu ohmic contact layer.