Ordered growth of Ge island clusters on strain-engineered Si surfaces

We report on the tailoring of the stress field distribution at the surface in a multilayered Ge/Si system in order to have a spontaneous ordering of the self-assembled islands in multi-island clusters. These clusters are ordered along [100]-[010] directions and arranged in a simple planar lattice. We investigate the evolution, from nucleation to ripening, of the Ge islands inside the clusters for two different stress modulations at the surface. The control over the stress at the surface has been obtained by tuning the last Si spacer layer thickness in a stacked-island multilayered structure. An appropriate selection of this spacer layer thickness allowed us to modulate the stress in two different limits of strong and weak island-island vertical interaction. We demonstrate that the stress modulation can be used to influence the island growth dynamics in order to induce an ordered spatial position of islands inside the cluster, to reduce the island size and to narrow the island size distribution