Nucleation and growth of ordered groups of SiGe quantum dots

An approach for the formation of ordered groups of Ge nanoislands (quantum dots, QDs) upon epitaxial growth on the surface of a heterostructure constituted by a Si (100) substrate having preliminarily formed seeds in the form of disk-like SiGe nanomounds is developed. It is found that the observed arrangement of QDs within a group is due to the anisotropic elastic-strain energy distribution on the surface of a SiGe nanomound, namely, to the existence of four local energy minima arranged in an ordered manner along the [100] and [010] directions with respect to the seed center. Multilayer structures with vertically aligned QD groups are grown using the suggested approach. The crystal structure and the elemental composition of the spatially ordered nanostructures are examined by transmission electron microscopy, X-ray diffraction analysis, and Raman spectroscopy.