Spontaneously forming nanostructures: Quantum dot molecules and rings

Annealing molecular beam epitaxy grown Ge/Si(100) islands spontaneously forms quantum dot molecules and rings. Quantum dot molecules (QDM) are close-packed arrays of several SiGe alloy hut clusters arranged with rectangular or circular symmetry. Rings are 3D structures with a depressed center. Both of these structures are related to island ensemble coarsening. Si interdiffusion into the perimeter of nominally pure Ge dome clusters forms a Si-rich annulus surrounding a Ge rich core. This lower melting point core diffuses away during coarsening of the island ensemble leaving behind the QDM. Large ring structures are formed by rapid coarsening of large, dislocated clusters during high temperature anneals.