Evolution of strained Ge islands grown on Si(111): a scanning probe microscopy study

We have followed the evolution of strained Ge/Si(111) Stranski-Krastanov islands by atomic force and scanning tunneling microscopies. Following the morphological evolution during the annealing of the samples we were able to recognize the key features of the relaxation process in these structures. The introduction of edge misfit dislocations after a critical thickness, and the inhomogeneous strain field inside the islands, lead to an intra-island ripening mechanism. We show that this mechanism changes the island shape from truncated tetrahedron to `atoll-like'