Highly transparent and low resistance gallium-doped indium oxide contact to p-type GaN

We report on a transparent gallium-doped indium oxide (GIO) ohmic contact to the p-GaN. The GIO contact film yielded a low specific contact resistance of 8.1×10−5Ωcm2 on p-GaN when annealed at 600 °C under a nitrogen ambient. The low specific contact resistance can be attributed to the formation of acceptorlike Ga vacancies and an InN or InxGa1−xN phase at the interface between the GIO and p-GaN films. The forward voltage of a light-emitting diode (LED) with a GIO ohmic layer was slightly increased by 0.2 V compared to that of a LED with a standard Ni∕Au contact. However, a light transmittance of 85.7%, which was higher than that of indium tin oxide, was observed in the GIO film at a wavelength of 470 nm after thermal annealing at 600 °C. These results suggest that the GIO contact scheme is suitable for use as a highly transparent and low specific contact resistance contact layer for p-GaN.