Nucleationless Three-Dimensional Island Formation in Low-Misfit Heteroepitaxy

The formation of faceted three-dimensional islands during growth of low-misfit ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ alloys on Si(100) has been investigated by low-energy electron microscopy. The formation of the islands in these alloy systems does not involve three-dimensional nucleation, but rather proceeds via a precursor array of shallow, stepped mounds on the surface that result from the inherent morphological instability of the strained alloy film.