Endotaxial Growth Mechanisms of Sn Quantum Dots in Si Matrix

Two distinct mechanisms for the endotaxial growth of quantum dots in the Sn/Si system were observed by means of analytical transmission electron microcopy. Both mechanisms operate simultaneously during temperature and growth rate modulated molecular beam epitaxy combined with ex situ thermal treatments. One of the mechanisms involves the creation of voids in Si, which are subsequently filled by Sn, resulting in quantum dots that consist of pure α-Sn. The other mechanism involves phase separation and leads to substitutional solid solution quantum dots with a higher Sn content than the predecessor quantum well structures possess. In both cases, the resultant quantum dots possess the diamond structure and the shape of a tetrakaidecahedron. (Sn,Si) precipitates that are several times larger than the typical (Sn,Si) quantum dot possess an essentially octahedral shape.