Fifteen phonon lines were observed in the first-order Raman spectrum of $6H$ SiC, using laser excitation. Polarized light was used to identify the mode symmetry, and a large-zone analysis was used to classify the modes and to display the results in what appear to be dispersion curves. All observed narrow lines are consistent with our interpretation, and only two of the expected lines remain unobserved. A study of the dependence of phonon energy on propagation direction shows that certain infrared and Raman active modes have extremely little infrared strength (a consequence of the polytype structure of $6H$ SiC). Doublets in the Raman spectrum give accurate measurements of the 4-8-${\mathrm{cm}}^{-1\mathrm{}}$ discontinuities within the large zone.

• Received 27 December 1967

DOI:https://doi.org/10.1103/PhysRev.170.698