Impact of the ZnO buffer on the optical properties of GaN: time resolved micro-photoluminescence

Spatially-resolved and time-resolved micro-photoluminescence (μ-PL) investigations were performed on thick GaN layers. Our measurements reveal that the peak position of the excitonic transition lines strongly depends on the distance to the substrate interface. The luminescence is shifted continuously to lower energies with decreasing distance, however, a strong blue shift occurs directly at the interface. The sample exhibits morphologically separated channels emitting at different energies and having different temporal behaviors. These different channels could be explained by the incorporation of O and Zn impurities, since ZnO buffer layers were used and disappeared after growing GaN on the substrate/buffer layer. Time-resolved luminescence investigations demonstrate that there is a strong energy transfer between the Zn and O channels.