Strain-induced self-organized growth of nanostructures: From step bunching to ordering in quantum dot superlattices

We have investigated the lateral ordering of dot positions in a SiGe/Si multilayer and, for comparison, in a PbSe/PbEuTe dot superlattice using grazing incidence small-angle scattering. The two samples represent two different approaches to achieve an enhanced ordering of dot positions in semiconductor heterostructures: in the SiGe/Si sample, step bunching in the multilayer grown on a vicinal Si substrate was exploited to reduce the fluctuations in lateral dot distances. In the PbSe/PbEuTe sample the strong elastic anisotropy leads to the formation of a three-dimensional dot "lattice," exhibiting a very narrow distribution of dot distances.