Free and Bound Excitons in GaN Epitaxial Films

Abstract

ABSTRACTWe report on photoluminescence experiments on hexagonal GaN epitaxial films grown on 6H-SiC and sapphire substrates by organo-metallic and hydide vapor phase epitaxy. At low temperatures we observe free and neutral donor bound exciton transitions which allow to establish properties of the free excitons and localisation energies of the bound excitons involving different shallow donors. From temperature dependent luminescence experiments thermal activation energies are determined which measure the exciton localization and donor binding energies. The localization energies of the excitons scale with the respective donor binding energies (Haynes rule). The inter-impurity transitions of neutral donors are observed in fourier transform infra-red absorption. Three shallow donors with binding energies of 34.7 meV, 55 meV and 58 meV can be seen. We present evidence for the chemical nature of the shallow impurities.