POLYTYPISM AND PROPERTIES OF SILICON-CARBIDE

The relationship between crystal structure and related material proper ties is discussed for the common 3C, 6H, 4H, and 2H polytypes of SiC. The theoretical results are derived in the framework of well converged density-functional calculations within the local-density approximatio n and the pseudopotential-plane-wave approach. In the case of electron ic excitations additionally quasiparticle corrections are included. Th e lattice-dynamical properties of the noncubic polytypes are described within a bond-charge model. We focus our attention on the actual atom ic structures, the accompanying lattice vibrations, thermodynamical pr operties, properties of layered combinations of polytypes, optical spe ctra, and surface equilibrium structures. On the one hand. the influen ce of the polytype on the material properties is considered. On the ot her hand, indications for driving forces of the polytypism are extract ed.