Ultraviolet Luminescence in Mg_0.12Zn_0.88O Alloy Films

We investigate the origin of ultraviolet (UV) emission from Mg_0.12Zn_0.88O alloy thin films with a wurtzite structure fabricated on c-plane Al₂O₃ substrates by plasma assisted molecular beam epitaxy. At room temperature, the absorption edge and UV emission band of the Mg_0.12Zn_0.88O film shift to high-energy side compared with ZnO films. Temperature dependence of the photoluminescence spectra shows that the UV emission is composed of free exciton and neutral donor bound exciton emissions. Two-step dissociation processes of the UV emission are observed with the increasing temperature. The thermal quenching mechanism is attributed to the dissociation of the free exciton from the neutral donor bound exciton in the low temperature region and the dissociation of free electron and hole from the free exciton in the high temperature region.