Effects of the lateral ordering of self-assembled SiGe nanoislands grown on strained Si$_{1-x}$Ge$_x$ buffer layers

Atomic-force microscopy, micro-Raman spectroscopy, and high resolution X-ray diffraction are applied to study the spatial ordering in single layers of SiGe nanoislands grown on a strained Si$_{1-x}$Ge$_x$ buffer sublayer. It is shown that, apart from stimulating the spatial ordering of nanoislands, the introduction of a Si$_{1-x}$Ge$_x$ sublayer leads to an enhanced role for interdiffusion processes. An unusually high increase in the volume of nanoislands in the process of the epitaxy is related to the anomalously strong diffusion from the buffer sublayer into the islands that is induced by nonuniform fields of elastic strains. The anisotropy of the islands shape and spatial ordering is discussed in terms of the anisotropy of the diffusion processes in spatially nonuniform fields of elastic strains.