THE PHONON-DISPERSION IN 6H-SIC INVESTIGATED BY INELASTIC NEUTRON-SCATTERING

Using coherent inelastic neutron scattering we have investigated the p honon dispersion relation of bulk hexagonal 6H-SiC. The complete set o f phonon branches has been determined along the Gamma-A and 14 out of 36 branches along the Gamma-M direction. The experimental data are com pared to ab initio calculations for cubic 3C-SiC transposed to 6H-SiC. Good agreement between theory and experiment is found for the Gamma-A direction. The discrepancies encountered for the Gamma-M direction ar e interpreted as evidence for a dependence of the dynamical response i n the SiC system on the stacking sequence.