Phonon strain-shift coefficients ofSi1−xGexgrown on Ge(001)

High germanium content ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$ alloys have been grown pseudomorphically at 400 °C on Ge (001) by molecular-beam epitaxy. The germanium fraction determined using x-ray diffraction measurements (x=0.8) is in good agreement with the value obtained with in situ x-ray photoemission results and vapor flux control. Combining Raman spectroscopy results and the epilayer stress value obtained by x-ray diffraction, we have determined the strain-shift coefficient (b) for each main Raman line (Ge-Ge, Si-Ge, and Si-Si). The variation of b is similar to the Grüneisen parameter (γ) alloy variation, i.e., b and γ values increase with increasing chemical disorder. The use of Raman scattering as a direct tool to determine the strain is discussed. The temperature dependence of the phonon frequencies has also been studied in the range from 300–5 K. © 1996 The American Physical Society.