Dielectric function and reflectivity spectrum of SiC polytypes

The frequency-dependent dielectric functions and reflectivity spectra of the cubic 3C and two hexagonal 2H and 6H polytypes of SiC are investigated by state-of-the-art ab-initio techniques. To this end, we employ a Green's function approach that enables us to include the relevant electronic correlation effects, in particular, the excitonic effects resulting from the electron-hole interaction. These two-particle correlation effects have a very significant influence on the optical properties. The resulting spectra are in good agreement with available experimental data while the spectra of independent-particle approaches show significant systematic deviations from experiment.