Determination of Germanium Content and Relaxation in Si1—xGex/Si Layers by Raman Spectroscopy and X-Ray Diffractometry

We determine the germanium content and degree of relaxation in heteroepitaxial Si1—xGex/Si layers through a combination of Raman spectroscopy and X-ray diffractometry. Our method uses the lattice constant a⊥ of the partially relaxed layer, as determined by double-crystal X-ray diffractometry, in combination with the Raman shift of the Si–Si vibrational mode. Samples with a Ge content of 0.20 < x < 0.35 and different relaxation values of 0 < R < 0.7 were chosen to verify the accuracy of the method. The lattice constant a⊥ was determined within an error range of ±5 × 10—4 Å using the angular distance between the 004 X-ray diffraction peaks of the epi-layer and substrate recorded in symmetrical Bragg geometry. With this value a⊥ and the Raman line shift of the Si–Si phonon, the values for the degree of relaxation and the Ge content are determined graphically from a chart based on a simple phenomenological model. The values obtained for x andRwere validated independently by X-ray diffractometry and agree to within ±0.01 for x and ±0.02 for R.