Polytypism and Properties of Silicon Carbide

The relationship between crystal structure and related material properties 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 approximation and the pseudopotential-plane-wave approach. In the case of electronic excitations additionally quasiparticle corrections are included. The lattice-dynamical properties of the noncubic polytypes are described within a bond-charge model. We focus our attention on the actual atomic structures, the accompanying lattice vibrations, thermodynamical properties, properties of layered combinations of polytypes, optical spectra, and surface equilibrium structures. On the one hand, the influence of the polytype on the material properties is considered. On the other hand, indications for driving forces of the polytypism are extracted.