Probing the lateral composition profile of self-assembled islands.

We apply a selective etching procedure to probe the lateral composition profile of self-assembled SiGe pyramids on a Si(001) substrate surface. We find that the pyramids consist of highly Si intermixed corners, whereas the edges, the apex, and the center of the pyramids remain Ge rich. Our results cannot be explained by existing growth models that minimize strain energy. We use a model that includes surface interdiffusion during island growth, underlining the paramount importance of surface processes during the formation of self-assembled quantum dot heterostructures in many different material systems.