Observation of optically-active metastable defects in undoped GaN epilayers

Abstract

Optically-active defects of undoped GaN epilayers grown on sapphire by metalorganic chemical vapor epitaxy was investigated with photoluminescence. A new metastable defect emitting blue light was found, besides the well-known yellow luminescence centers. With excitation by the 325 nm He–Cd laser, this metastable defect, at low temperature, exhibits the luminescence fatigue effect with the decay time determined to be about 6 min. When the temperature is increased to room temperature, it recovers its optically-active state. The yellow band emission increases in intensity as the blue band emission decreases in intensity. Analysis shows that this metastable center is a hole trap, and Ga vacancy is its most probable candidate.