The interaction of phonon states with the point, line, and plane defects is considered near the edge of an optical-phonon branch. Because the effect of disorder on optical phonons is ordinarily studied in the Raman experiments, we calculate the averaged phonon Green’s function characterizing the Raman line shape. There are two frequency regions in the Raman spectra: the first involves excitations of an extended phonon mode and the second corresponds with a phonon state localized on defects. We find broadening and line-shape asymmetry of the extended mode due to scattering by defects. On the other hand, the contribution of localized states to Raman spectra has a form of shoulder with a width proportional to the square root of the defect concentration.

• Received 19 December 2000

DOI:https://doi.org/10.1103/PhysRevB.64.024301