On the driving forces for the vertical alignment in nitride quantum dot multilayers

The layer-to-layer vertical alignment of GaN quantum dots in AlN multilayers is quantified as a function of the spacer layer thickness and the number of bilayers, using grazing-incidence X-ray scattering. Although the density of dots is comparable to the density of (0001) threading dislocations, we observe that the strong vertical ordering is strain induced by the buried dots. Elasticity theory calculations confirm this experimental result and explain the observation of the exceptionally strong vertical alignment in nitride compared to other classical systems.