MICROSTRUCTURAL EVOLUTION DURING THE HETEROEPITAXY OF GE ON VICINAL SI(100)

Microstructural evolution during the initial stages of islanding of Ge on vicinal Si(100) has been studied in situ with nanometer resolution in an ultrahigh-vacuum scanning transmission electron microscope. Ge is deposited using molecular-beam-epitaxy (MBE) techniques on vicinal Si(100) misoriented 1-degrees and 5-degrees toward <110>. For MBE-type experiments, there is evidence for metastable growth of the Ge intermediate layer to much greater than the equilibrium critical thickness. The layer may grow up to seven monolayers thick before islanding in the Stranski-Krastanov growth mode. The presence of strong adatom sinks significantly alters the growth and size distribution of the islands when the spacing of these sinks is less than an adatom diffusion distance. Studies of the initial stages of islanding in solid-phase MBE indicate that there is no long-range adatom diffusion. There is an initial fast transformation from a disordered layer growth, followed by a sluggish growth of islands. We have studied the coarsening of these islands at the earliest stages with sensitivity to islands as small as 2 nm in radius. It appears that there is a novel coarsening mechanism influenced by an unstable intermediate layer and dislocation-free islands. In all cases, the dislocation-free islands grow more slowly than those which have relaxed by the introduction of misfit dislocations.