2ND-ORDER RAMAN-SPECTRA OF SIC - EXPERIMENTAL AND THEORETICAL RESULTS FROM AB-INITIO PHONON CALCULATIONS

We report experimental and theoretical low-temperature second-order Raman spectra of 3C-SiC. Similar to the spectra of other group-IV and III-V semiconductors the GAMMA1 spectrum is strong, and the GAMMA12 and GAMMA15 spectra are very weak. The theoretical Raman spectra have been calculated using ab initio phonon eigensolutions and phenomenological polarizability coefficients. Good agreement between theory and experiment has been obtained. The GAMMA1 spectrum exhibits three distinct peaks at 1302, 1400, and 1619 cm-1 which occur in the gaps of the overtone density of states. This exemplifies the importance of taking into account the coupling matrix elements rather than simply relying on the one-to-one correspondence between the overtone density of states and the GAMMA1 Raman spectrum, which is commonly done for ZnS-type semiconductors.