ELECTRONIC-PROPERTIES OF CUBIC AND HEXAGONAL SIC POLYTYPES FROM AB-INITIO CALCULATIONS

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