Transparent Ohmic Contacts on p‐GaN Using an Indium Tin Oxide Overlayer

We report a low-resistant, thermally stable ohmic contact on p-GaN using a promising contact scheme of Ni/Au/ITO. Ni/Au contact on p-GaN was annealed at 500 °C under an oxidizing atmosphere before ITO deposition, forming a NiO layer acting as a diffusion barrier of In atoms from ITO. Specific contact resistivity as low as 4.8 × 10—4 Ωcm2 was obtained from the Ni (20 Å)/Au (30 Å)/ITO (1000 Å) contact annealed at 500 °C under an oxidizing atmosphere. Contact resistivity is decreased due to crystallization of ITO and Au indiffusion through the NiO layer after annealing at 500 °C under an oxidizing ambient. Also, under this condition, the measured optical transmittance of Ni/Au/ITO was above 80% at a wavelength of 470 nm.