The phonon spectra of substitutional C defects were studied for a wide range of Ge contents. The 3-fold degenerate localized phonon mode of the C defects was found to split, into a number of phonon modes, with changes in composition. The split-off modes appeared due to warping of the defect symmetry, while various nearest-neighbour atomic environments of Si and Ge atoms formed around substitutional C atoms. The phonon spectra were simulated by using a Keating model which took account of the effects of C anharmonicity. The results of the calculations were in good agreement with experiment.

Phonon Spectra of Substitutional Carbon in SiGe Alloys L.V.Kulik, C.Guedj, M.W.Dashiell, J.Kolodzey, A.Hairie: Physical Review B, 1999, 59[24], 15753-9