We theoretically investigate elastic, piezoelectric and optical properties of wurtzite GaN/AlN quantum dots, having hexagonal pyramid-shape, stacked in a multilayer. We show that the strain existing in quantum dots and barriers depends significantly on the distance between the dots i.e. on the width of AlN barriers. For typical QDs, having the base diameter of 19.5nm, the drop of the electrostatic potential in the quantum dot region slightly decreases with decreasing of the barrier width. This decrease is however much smaller for QDs than for superlattice of GaN/AlGaN quantum wells, with thickness similar to the height of QDs. Consequently, the band-to-band transition energies in the vertically correlated GaN/AlN QDs show unexpected, rather weak dependence on the width of AlN barriers. Increasing the QD base diameter leads to stronger decreasing dependence of the band-to-band transition energies vs. the width of AlN barriers, similar to that observed for superlattieces of QWs.

An investigation of 1–5 nm in diameter indium rich clusters in MOCVD InxGa1-xN/GaN quantum well is carried out. To this end, quantitative High Resolution Transmission Electron Microscopy (HRTEM) is coupled with the Finite Element Method (FEM) for the calculation of thin foil relaxation and for image simulation. The measurement of the tetragonal distortion from HRTEM images is a useful tool for the determination of chemical composition in heterostructures. However, for a correct interpretation of the measured lattice distortion on HRTEM images, one needs to take into account the strain averaging across TEM sample and inhomogeneous relaxation of the sample. As a first step, 3D FEM simulation of the relaxation process as a function of the position of indium rich cluster relative to the foil surface is performed. Next, the calculated 3D displacement field is used to simulate the HRTEM images. The results clearly show that the magnitude of the strain field depends on the cluster position. It is concluded that the HRTEM images of indium rich clusters can differ even for the same indium content due to different positions of the clusters.