Phonon spectra of substitutional carbon in Si1-xGex alloys

The phonon spectra of substitutional carbon defects in Si1-xGex alloys are studied over a broad range of Ge contents. With changing composition, the t hreefold-degenerate localized phonon mode of carbon defects in silicon was found to split into a number of phonon modes. The split-off modes appear du e to the warping of defect symmetry while different nearest atomic environm ents of silicon and germanium atoms form around substitutional carbon atoms . The phonon spectra are simulated with a Keating model, taking into accoun t the effects of carbon anharmonicity. The results of calculations are in g ood agreement with experiments. [S0163-1829(99)03724-8].