Second-order Raman spectra of SiC: Experimental and theoretical results fromab initiophonon 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 Γ₁ spectrum is strong, and the Γ₁₂ and Γ₁₅ 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 Γ₁ 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 Γ₁ Raman spectrum, which is commonly done for ZnS-type semiconductors.