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

We report experimental and theoretical low-temperature second-order Ra man spectra of 3C-SiC. Similar to the spectra of other group-IV and II I-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 experi ment has been obtained. The GAMMA1 spectrum exhibits three distinct pe aks at 1302, 1400, and 1619 cm-1 which occur in the gaps of the overto ne density of states. This exemplifies the importance of taking into a ccount the coupling matrix elements rather than simply relying on the one-to-one correspondence between the overtone density of states and t he GAMMA1 Raman spectrum, which is commonly done for ZnS-type semicond uctors.