Wave-vector dependence of Raman scattering intensity in folded modes of long-periodα-SiC

It is found that the relative Raman intensity of several folded transverse-acoustic modes in silicon carbide polytypes varies markedly with the scattering wave vector q of the phonons under off-resonance conditions. A simple expression for the q-dependent intensity of Raman scattering is derived, based on the bond-polarizability concept. Using atomic displacements obtained from a linear-chain model, the variation of the intensity with q is calculated. The results agree well with the experimental results for 6H, 8H, 15R, and 21R polytypes. This agreement indicates that the bond polarizability approximation is valid for {α}-SiC.