Temperature Dependence and High-Temperature Stability of the Annealed Ni/Au Ohmic Contact to p-Type GaN in Air

We report on the temperature-dependent contact resistivity and high-temperature stability of the annealed Ni/Au ohmic contacts to p-type GaN in air. As the measure temperature increases from 25°C to 390°C, both the specific contact resistivity (ρ_c) and sheet resistance (R_sh) decrease by factors ∼10, contributing to the 10-fold increase in current at 390°C compared with that at 25°C. It was also observed that the ρ_c was further reduced by 36%, i.e., from 2.2 × 10⁻³ Ω cm² to 1.4 × 10⁻³ Ω cm², during the 48-h high-temperature stability test at 450°C in air, showing excellent stability of the contacts. An increase in ρ_c was observed after the contacts were subjected to 500°C in air. Higher temperature stress led to a significant increase in ρ_c. The contacts show rectifying I–V characteristics after being subjected to 700°C for 1 h. The degradation mechanics were analyzed with the assistance of transmission electron microscopy and energy dispersive x-ray spectroscopy.