Phonon Raman scattering in disordered silicon carbides

A study has been conducted of the spectra of Raman scattering in silicon carbide crystals containing stacking disorders. The Raman bands of these crystals exhibit broadening, distortion and asymmetry in their band shape. For heavily disordered Sic, a broad low-frequency tail appears in the region of the transverse acoustic phonon energy. Raman intensity profiles are calculated for models of the disordered structure, which consider the structure as an extreme case of long-period polytypes. The calculated Raman spectra are compared with the experimental spectra of the disordered Sic crystals. The comparison indicates that the broadening and distortion of the Raman bands in the disordered SiC are dominated by the relaxation of the wave-vector conservation rule. Also the spectral shape was found to depend on the stacking structure of the domains existing in the crystals, on the average size of the domains and also on the distribution of the domain sizes. X-ray diffraction measurements support the Raman scattering analysis. It is concluded that Raman intensity analysis can be useful in evaluating stacking disorders in SiC crystals.