Lateral and vertical ordering in multilayered self-organized InGaAs quantum dots studied by high resolution x-ray diffraction

We have studied multiple layers of self-organized InGaAs-islands grown on GaAs by x-ray diffraction reciprocal space mapping. We found an anisotropy of the dot spacing in [100] and [110] direction consistent with an ordering of the dots in a two-dimensional square lattice with main axes along the [100] direction and a lattice parameter of 55 nm. The nearly perfect vertical alignment (stacking) of the dots was deduced from the diffraction peak shape.