Persistent photoluminescence in high-purity GaN

Abstract

High-purity GaN grown by hydride vapor-phase epitaxy was studied by time-resolved photoluminescence (PL). Two types of samples, 6–30-μm-thick GaN layers on sapphire substrate and a 200-μm-thick freestanding template, exhibited similar PL behavior. At low temperatures, the luminescence signal from the red, yellow, blue, and ultraviolet luminescence bands could be detected at delay times up to several minutes following excitation light pulse. The persistent PL in freestanding template can be attributed solely to a donor–acceptor-pair-type recombination in very pure GaN. However, a similar slow decay of radiative transitions in apparently less-pure GaN films on sapphire raises the possibility of additional mechanisms for the observed persistent PL.