Enhancement of light reflectance and thermal stability in Ag-Cu alloy contacts on p -type GaN

The mechanism for thermally stable Ag-Cu alloy Ohmic contact on p -type GaN was investigated. Ag-Cu contact showed lower contact resistivity as low as 8.6 × 10 − 6 Ω cm 2 , higher reflectance of 84% at 460 nm , and better thermal stability than Ag contact after annealing in air ambient. The formation of Ag-Ga solid solution lowered the contact resistivity. Additionally the formation of Cu oxide suppresses the Ag oxidation and increases the work function of the Ag-Cu contact via decreasing the Schottky barrier height for hole injection. Precipitation of Cu oxide at grain boundaries suppresses the Ag agglomeration, leading to enhanced light reflectance as well as thermal stability.