Growth morphology and the equilibrium shape: The role of "surfactants" in Ge/Si island formation.

Surface energy anisotropy, as opposed to surface energy, is shown to influence changes of growth mode in Ge/Si by «surfactant» impurities. By annealing thin Ge/Si films, we find the equilibrium island shape, and hence the surface energy anisotropy; radical changes in shape are seen for impurity-terminated surfaces: Ge:Sb enhances (100) facets compared to clean Ge and Ge:In favors {311}. Thus Sb impurities favor large flat islands which would lead to earlier island coalescence and can aid planar (100) growth, while In (though otherwise a good «surfactant») leaves the film faceted