Finite element analysis of the strain induced vertical ordering of islands and determination of compositional modifications in LPCVD-grown Ge_xSi_1−x-Si bilayers on Si(001)

Abstract

The vertical ordering of Ge^xSi^1-x islands along the growth direction during low pressure chemical vapour deposition of Ge^xSi^1-x-Si bilayers on Si[001] is studied by transmission electron microscopy and analysed quantitatively using finite element method simulations. The calculation of local strain fields and the determination of an island correlation function allows one to describe the observed ordering behaviour in terms of a strain induced preferential nucleus formation above existing islands. In addition the compositions of the Ge^xSi^1-x layers are measured by a lattice fringe analysis of high-resolution transmission electron micrographs giving clear evidence for a substantial silicon germanium intermixing. The implications of these compositional modifications for the nucleation and ordering of islands are discussed indicating that islands are subjected to geometrical and compositional modifications during the growth process.