The formation of faceted three-dimensional islands during growth of low-mis
fit Si1-xGex alloys on Si(100) has been investigated by low-energy electron
microscopy. The formation of the islands in these alloy systems does not i
nvolve three-dimensional nucleation, but rather proceeds via a precursor ar
ray of shallow, stepped mounds on the surface that result from the inherent
morphological instability of the strained alloy film.