Localized phonon states at the edge of the continuous spectrum

An analysis is made of the influence of defects on the averaged Green’s function of optical phonons whose imaginary part is proportional to the cross section for Raman one-phonon light scattering, which depends on the frequency transfer. A variant of the “cross” technique which can take into account the localized states at defects is used. The defects are assumed to be two-dimensional (of the dislocation type) at which localized states exist near the edge of the continuous spectrum interacting weakly with the defect. As a result of this interaction, which depends on the defect concentration, the states of the continuous spectrum are shifted and broadened, the inhomogeneous broadening depending strongly on the frequency transfer (phonon density of states effect), which leads to asymmetry of the Raman line. The defect concentration also influences the localized states which interact mainly via band states.