Raman study of isotope effects and phonon eigenvectors in SiC

We have measured Raman spectra of several SIC polytypes (3C, 6H, 15R) made from natural silicon (approximate to(28)Si) and Si-30. The isotope shifts o f the phonon frequencies show characteristic variations with their effectiv e wave vector in the zinc blende (3C) modification which arises from Brillo uin zone backfolding. This allows us to determine the phonon eigenvectors o f 3C SiC for the dispersion branches along the [111] direction. The observe d magnitudes of the Si and C ion displacements, as well as their relative p hase, confirm bond charge model and ab initio calculations. [S0031-9007(99) 08863-8].