PHONON RAMAN-SCATTERING IN DISORDERED SILICON CARBIDES

A study has been conducted of the spectra of Raman scattering in silic on carbide crystals containing stacking disorders. The Raman bands of these crystals exhibit broadening, distortion and asymmetry in their b and shape. For heavily disordered SiC, a broad low-frequency tail appe ars in the region of the transverse acoustic phonon energy. Raman inte nsity profiles are calculated for models of the disordered structure, which consider the structure as an extreme case of long-period polytyp es. The calculated Raman spectra are compared with the experimental sp ectra of the disordered SiC crystals. The comparison indicates that th e broadening and distortion of the Raman bands in the disordered SiC a re dominated by the relaxation of the wave-vector conservation rule. A lso the spectral shape was found to depend on the stacking structure o f the domains existing in the crystals, on the average size of the dom ains and also on the distribution of the domain sizes. X-ray diffracti on measurements support the Raman scattering analysis. It is concluded that Raman intensity analysis can be useful in evaluating stacking di sorders in SiC crystals.