Polarity dependent properties of GaN layers grown by hydride vapor phase epitaxy on GaN bulk crystals

Hydride vapor phase epitaxy (HVPE) was used to grow nominally undoped 30-160 mum thick GaN layers on both the Ga and N polar sides of high pressure grown single crystal GaN substrates. Measurements of photoluminescence, infrared reflectivity, mu-Raman scattering and positron annihilation were performed on the samples. The obtained characteristics are strongly dependent on the growth polarity. The material grown on the N polar side has identical properties with the substrate bulk GaN crystals, i.e. high free electron, impurity and point defect concentrations. In the layers grown on the Ga polar side, these concentrations are very low. The results show that the structural and optical properties of hormoepitaxial GaN layers grown by HVPE are homogeneous across the layer thickness, which is in contrast to the heteroepitaxial HVPE GaN layers.