Low‐Resistance, High‐Transparency, and Thermally Stable Ohmic Contacts on p‐Type GaN Using Ru and Ir

Low-resistance, high-transparency, and thermally stable ohmic contacts on p-type GaN were achieved using Ru- and Ir-based metallization through oxidation annealing. A contact resistivity of ∼4 × 10—5 Ωcm2 and a high light transmittance of ∼85% were obtained from oxidized Ru (50 Å)/Ni (50 Å) and Ir (50 Å)/Ni (50 Å) contacts. The formation of a RuO2 (or IrO2)/p-GaN contact reduced the effective Schottky barrier height for hole injection and a NiO layer at the surface suppressed the outdiffusion of free Ga and N atoms, resulting in a reduction of the contact resistivity. The fully oxidized contact structure of NiO/RuO2 (or IrO2)/p-GaN enhanced the light transmission and the thermal stability simultaneously.