Vertically self-organized Ge/Si(001) quantum dots in multilayer structures

In situ reflection high-energy electron diffraction along with transmission electron miscoscopy, atomic force microscopy, and photoluminescence spectroscopy have been used to investigate the Ge growth behavior in a standard Ge/Si multilayer structure. It is shown that the decrease of the Ge wetting layer thicknesses in the upper layers of a multilayer structure is the main parameter which leads to the increase of the island size and height. Such an evolution of the Ge wetting layer thickness can be explained by an accumulation of elastic strain in the Si spacer layers induced by the lower Ge wetting layers. This finding opens the route to the realization of a multilayer structure in which the islands have equal size in all layers.