Spatially-Resolved Photoluminescence and Raman Study on the GaN/Substrate Interface

We performed spatially-resolved photoluminescence and Raman experiments on the substrate interface region of wurtzite GaN layers. We found that the broad ”yellow” photoluminescence band is strong only near the interface. Our investigations reveal that both the substrate interface and a region of structural reorientation of the layer near the interface act as source of the photoluminescence. The Raman-scattering experiments show that at least a portion of the GaN layer near the substrate interface is oriented in such a way that the c-axis of the layer is parallel to the substrate interface. At a distance about 30 µm away from the interface the layer reorients by turning the c-axis by 90° into a direction perpendicular to the substrate interface.