Optical properties of GaN/AlGaN quantum wells grown on nonpolar substrates

In this paper we report on the optical properties of a series of GaN/AlGaN multiple quantum well structures grown on a-plane (11 (2) over bar0) GaN, which had been deposited on r-plane (1 (1) over bar 02) sapphire substrates, compared to a reference GaN template of the same orientation. The low temperature photoluminescence spectrum of the template layer is dominated by two emission bands, which we attribute to recombination involving excitons in the bulk of the layer and electrons and holes trapped at basal-plane stacking faults, designated X1 and X2, respectively. The photoluminescence spectra from the quantum well structures show similar emission bands except that both X1 and X2 shift to higher energy with decreasing quantum well thickness. The shift to higher energy is due to the effects of quantum confinement on carriers trapped at the stacking faults that intersect the quantum wells, as well as those excitons that are localized within the quantum wells. This assignment is based partly on excitation spectroscopy that reveals exciton transitions associated with electrons from the n=1 and n=2 quantum well confined states. (c) 2008 American Institute of Physics.