Void-mediated formation of Sn quantum dots in a Si matrix

Abstract

Atomic scale analysis of Sn quantum dots (QDs) formed during the molecular beam-epitaxy (MBE) growth of ${\mathrm{Sn}}_x{\mathrm{Si}}_{\text{1−x}}\text{\hspace{0.05em}(0.05⩽x⩽0.1)}$ multilayers in a Si matrix revealed a void-mediated formation mechanism. Voids below the Si surface are induced by the lattice mismatch strain between ${\mathrm{Sn}}_x{\mathrm{Si}}_{\text{1−x}}$ layers and Si, taking on their equilibrium tetrakaidecahedron shape. The diffusion of Sn atoms into these voids leads to an initial rapid coarsening of quantum dots during annealing. Since this formation process is not restricted to Sn, a method to grow QDs may be developed by controlling the formation of voids and the diffusion of materials into these voids during MBE growth.