Morphology and photoluminescence of Ge islands grown on Si(001)

The use of self-organization of nanostructures during growth of materials h aving a high lattice mismatch e.g. Ge on Si offers new possibilities for de vice applications. The Ge layers were grown on Si(001) substrates by low pr essure chemical vapour deposition. Island size statistics derived from the atomic force micrographs show a trimodal size distribution at high average Gr layer thicknesses, whereas at low Ge layer thicknesses only a narrow mon omodal island size distribution exists. Transmission electron micrographs r eveal the type of relaxation of the Ge islands and the shape of islands aft er being capped by a Si overlayer. A correspondence beta cen the broadening of the spectral emission and the island morphology can be concluded from p hotoluminescence measurements. Multiple stacked island layers exhibit a sig nificant increase of integral intensity in comparison with a single layer o f islands, grown under equal conditions. A clear vertical correlation betwe en island positions in different lavers and a continuous enlargement of isl and size in upper layers is found on transmission electron micrographs of s tacked island layers. (C) 1998 Elsevier Science S.A. All rights reserved.