Nature and elimination of yellow-band luminescence and donor–acceptor emission of undoped GaN

The nature of yellow-band luminescence (YL) and donor–acceptor (DA) emissions of undoped GaN grown on sapphire or laterally overgrown on patterned ${\mathrm{Si}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}}$ was investigated using low-temperature photoluminescence and spatially resolved photoluminescence. The states, producing the levels responsible for the YL and DA emissions, arise from complexes of extended defects and native-point defects (most likely Ga vacancies) or impurities (such as carbon). For GaN directly grown on a low-temperature-grown GaN buffer layer, the YL and DA emissions can be eliminated by simply increasing the buffer-layer growth temperature as the result of enlarging hexagonal crystallites, and consequently, reducing the density of extended defects. For laterally overgrown GaN, a much lower density of extended defects substantially suppresses the YL emission.