Island formation and faceting in the SiGe/Si(0 0 1) system

The formation and evolution of coherently strained three-dimensional islands during epitaxial growth of SiGe on Si(0 0 1) was investigated by scanning tunneling microscopy. Si1−xGex layers a few nanometers thick were grown by magnetron sputter epitaxy at a substrate temperature of about 600 °C in a composition range x between 0.3 and 1. Islands first appear as shallow unfaceted mounds on a rough wetting layer. Subsequently, small {1 0 5} facets are introduced close to the regions of steepest slope on each mound. The {1 0 5} facets then expand, leading the mounds to gradually transform into truncated pyramids and eventually into completely faceted pyramids or slightly elongated hut-clusters bounded by four {1 0 5} facets. Trenches surround large pyramids. Islands at different stages of their evolution are observed to coexist and to ripen during growth or post-growth annealing at 600 °C.