Study of molecular-beam epitaxially grown Ge_xSi_1-x/Si layers by Raman scattering

The strain distribution of a Ge_xSi_1-x/Si strained layer superlattice (SLS) as a function of the distance from the superlattice/substrate interface has been studied by Raman spectroscopy. A small-angle bevel was made by angle lapping on a given thick Ge _xSi_1-x/Si SLS so that it is possible to probe the structure at different thicknesses. The Raman spectrum as a function of the distance from interface is then obtained. The results indicate that, as we move away from the substrate interface, the compression strain in the alloy layers decreases while the tensile strain in the Si layers increases. From linewidth measurement of the Raman peaks, it appears that there is an improved crystal quality and a lower concentration of defects going away from the substrate interface.