Raman spectroscopy determination of composition and strain in Si1-xGex/SiSi1-xGex/Si heterostructures

A procedure for the quantitative measurement of composition and strain in epitaxial Si1-xGex/SiSi1-xGex/Si heterostructures by means of Raman spectroscopy for any Ge concentration is presented. The calibration of the parameters of this procedure involved the growth of a set of heteroepitaxial layers spanning the range from pure Si to pure Ge. Different strain conditions were established in a highly controlled way by tailoring the substrate lattice parameter. Through the comparative analysis of reciprocal space mapping and Raman spectroscopy we obtained a set of parameters for the phonon energy variation due to biaxial deformation, as well as calibration curves for the dependence of the Raman band frequencies on alloy composition. With these new calibrations, Raman spectroscopy provides an accuracy in the determination of composition and strain comparable to that of X-ray diffraction, but with the added advantage of high-spatial resolution and resonance-induced surface confinement.