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 Si3N4 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. (C) 1999 American Institute of Physics. [S0003-6951(99)04019-X].