Local structure of strain-compensated epitaxial Si 1− x− yGe xC y layers on Si(001) grown with molecular beam epitaxy

Abstract

We show that it is possible to adjust the strain in pseudomorphic SiGe layers on Si(001) by adding small amounts of carbon. A strain-free Si 1− x− y Ge x C y layer can be grown on Si(001) by choosing the concentrations x and y such that the volume changes due to the germanium and carbon atoms compensate. The local atomic structure and lattice dynamics of a strain-compensated layer are studied. Experimental and theoretical results are compatible with Vegard's rule. To handle the large bond length distortion near C atoms properly, the used valence-force field model includes anharmonic effects via bond length dependent interatomic force constants which were determined from ab initio density-functional calculations. The dependence of Raman spectra on strain and composition of Si 1− x− y Ge x C y layers can be explained by the model calculations.