Raman Scattering from Anisotropic Phonon Modes in SiC Polytypes

Frequency difference between planar and axial type modes in transverse optical phonons has been studied in various SiC polytypes by Raman scattering. The degree of the anisotropy in the phonon frequency is closely correlated with percent of the hexagonal stacking in polytypes. It is confirmed experimentally that the proportionality between the anisotropy and hexagonality holds for all the polytypes identified by X-ray analysis. The calculation under the assumption that the interplanar force constant differs for hexagonal and cubic environments has explained this relationship. These results suggest that the hexagonality of unidentified polytypes with longer period can be determined from Raman measurements of the anisotropy. Optical phonons in 2H–SiC have also been examined and their frequencies have been obtained.