Strain engineering in Si via closely stacked, site-controlled SiGe islands

The authors report on the fabrication and detailed structural characterization of ordered arrays of vertically stacked SiGe/Si(001) island pairs. By a proper choice of growth parameters, islands which have both large sizes and high Ge fraction are obtained in the upper layer. Finite element method calculations of the strain distribution reveal that (i) the Si spacer between a pair of islands can act as a lateral quantum dot molecule made of four nearby dots for electrons and (ii) the tensile strain in a Si cap deposited on top of the stack is significantly enhanced with respect to a single layer.