Vertical and lateral ordering of Ge islands grown on Si(001): theory and experiments

Abstract

A set of recent results concerning lateral and vertical ordering of Ge islands grown onSi(001) is reviewed. Experimental data generated by chemical vapour deposition andanalysed by atomic force microscopy and photoelectron spectroscopy are compared withcomputer simulations and modelling based on atomistic approaches and continuum theory.In particular, we show that it is possible to probe experimentally the detailedstrain field generated by buried Ge islands at the surface of the Si capping layer.The observed arrangement of small Ge islands grown over the capping layer isdemonstrated to be very close to the one predicted by a simple model where the localchemical potential is inferred from the strain field at the atomic scale, as given byTersoff-potential molecular dynamics simulations. Moreover, we review recentexperimental evidence for lateral ordering, triggered by partial Si capping, in thefirst layer of Ge islands on Si(001). Theoretical support is given by showing thatwhen two islands lie in close proximity the elastic field is likely to generate aflow of atoms leading to an effective gliding motion along opposite directions ofboth islands, eventually stopped by the presence of further neighbouring islands.