Ohmic and degradation mechanisms of Ag contacts on p-type GaN

The electrical and optical properties of the Ag contacts have been investigated as a function of the annealing temperature. The as-deposited contact becomes good Ohmic with contact resistivity of 2.47 × 10 ^-4 Ω cm² and produces reflectance of ∼84% when annealed at 330°C for 1 mm in air ambient. However, annealing at 530°C results in nonlinear current-voltage behavior and degraded reflectance. The light output of InGaN/GaN blue light emitting diodes (LEDs) fabricated with the as-deposited Ag contact shows somewhat better output performance than those of LEDs with the annealed Ag contacts. Based on the transmission electron microscopy-energy dispersive x-ray analysis, synchrotron x-ray diffraction, and x-ray photoemission spectroscopy results, possible mechanisms for the ohmic formation and degradation of the Ag contacts are described.