Formation of one-dimensional surface grooves from pit instabilities in annealed SiGe/Si(100) epitaxial films

Growth of Si_0.7Ge_0.3 on Si under kinetically limited conditions results in the formation of shallow strain-relieving pits that only partially penetrate the wetting layer. Upon annealing at the growth temperature of 550°C, these pits elongate in one of the <100> directions and obtain near-{105} facets. The length-to-width aspect ratio of the resulting grooves can be as large as 20. Material ejected from the pits accumulates along the sides of the elongated pit forming shallow islands with a shape that exhibits a monotonic dependence on island size, and eventually evolves to {105} facets. We discuss the origins of this roughening behavior, which may provide a route for self-assembly of highly anisotropic quantum nanostructures.