Cathodoluminescence and Micro-Raman Characterisation of GaN/AlN QDs Grown on Si (111)

GaN/AlN based heterostructures made of stacked GaN QDs have been studied by means of cathodolumi-nescence (CL) and micro-Raman techniques. The number of stacked layers varied between 2 and 85 in the studied samples. The QDs emission has been revealed by cross sectional CL spectra, confirmed by the high blue shift with increasing injection conditions. In-plane depth resolved CL has shown the contribu-tion from aggregates of QDs with different average size along the growth direction. Micro-Raman data al-lowed to obtain information about the strain fields present in the layers. Relaxation process seems to occur, depending on the structural characteristics of the samples. The complementary information given by the two optical techniques allowed a better understanding of the contributions affecting the QDs emis-sions, such as the QD sizes, the strain levels or the effect of the internal electric fields.