Self-Assembled 3D Morphology of Buffer Layers and Influence on Luminescence and Defect Formation in InGaN/GaN Quantum Wells

We have prepared a set of samples comprising 40 InGaN/GaN quantum wells (QWs), all of which were grown by using the same technological procedure. However, the samples differ in terms of their surface morphology, as they were grown on four different types of buffer layers. Although the MQW region was prepared in the same way, the properties and characteristics of the samples differ significantly. We demonstrate that growing the MQW region on a surface fully covered by V-pits with semipolar facets improves the photoluminescence (PL) properties, particularly for samples with high dislocation densities. Our results suggest that 3D buffer layer morphology can be advantageous for growing GaN-based LEDs on Si substrates, where a high dislocation density cannot be avoided. This is due to the formation of different defects on a flat surface compared with a surface covered with semipolar facets. To elucidate the correlation between PL properties and defect formation, the samples were characterized using various techniques, including SEM, photoluminescence spectroscopy, time-resolved photoluminescence, spectrally and spatially resolved cathodoluminescence, thermally stimulated luminescence, and, for selected samples, cross-sectional STEM. Vacancy-related defect formation was studied for the first time for thick InGaN/GaN MQW structures by variable-energy positron annihilation spectroscopy.