Electronic properties of cubic and hexagonal SiC polytypes fromab initiocalculations

Ab initio total-energy studies are used to determine the lattice constants and the atomic positions within the unit cells for 3C-, 6H-, 4H-, and 2H-SiC. The electronic structures are calculated for the atomic geometries obtained theoretically within the density-functional theory (DFT) and the local-density approximation (LDA). We state more precisely the ordering of the conduction-band minima and derive effective masses. By adding quasiparticle corrections to the DFT-LDA band structures we find indirect fundamental energy gaps in agreement with the experiment. A physical explanation of the empirical Choyke-Hamilton-Patrick relation is given. Band discontinuities, bandwidths, crystal-field splittings, and ionic gaps are discussed versus hexagonality.