Stability of alloyed and nonalloyed ohmic contacts to n-type GaN at high temperature in air

We report on the higherature characteristics and stability of both alloyed Ti/Al/Ni/Au ohmic contacts and nonalloyed Al/Au ohmic contacts to n-type GaN at temperatures up to 600 °C in air. The alloyed contacts showed a specific contact resistivity (ρ_c) of 6.8 - 10^-6 Ω cm² at room temperature after fabrication. ρ_c did not change with temperature or show degradation after the application of thermal stress at 600 °C for 4 h in air. The ρ_c of nonalloyed contacts was reduced by two orders of magnitude and stabilized to 5 - 10^-6 Ω cm² after the application of higherature thermal stress. Transmission electron microscopy, scanning transmission electron microscopy, and electron energy loss spectroscopy were used to analyze the metal-semiconductor interface to understand the formation of the low-resistivity and high-stability ohmic contacts at high temperature. Our study reveals the high stability of both alloyed and nonalloyed ohmic contacts for GaN-based electronic devices operating at high temperatures in air.