Optical and loss spectra of SiC polytypes from ab initio calculations

Frequency-dependent dielectric functions are calculated for the hexagonal polytypes 2H,f4H, and 6H as well as the cubic modification 3C of silicon carbide. The calculations are based on the ab initio pseudopotential-plane-wave method and random-phase approximation. We find a remarkable redistribution of the optical absorption and related spectra as reflectivity and energy loss due to the variation of the crystal structure and polarization direction. The relation of spectra and underlying electronic structures as well as the influence of nonlocality and quasiparticle effects are discussed. The numerical results are compared with experimental data available.