Raman intensity profiles of folded longitudinal phonon modes in SiC polytypes

Raman spectral profiles of folded longitudinal phonon modes in 4H-, 6H-, an d 21R-SiC polytypes which form natural superlattices have been studied expe rimentally and theoretically. The Raman intensity of the folded longitudina l modes is very weak except for the mode corresponding to a zone-center pho non mode in the 3C polytype. The intensity profiles of these modes are inte rpreted on the basis of;the bond polarizability concept when one takes into account difference of the bond Raman polarizability between the cubic and hexagonal environments. The agreement of the measured and calculated intens ities indicates that the bond polarizability model can be applied to Raman spectral profiles of the longitudinal folded modes as well as transverse fo lded modes in SiC.