Properties of interfaces between cubic and hexagonal polytypes of silicon carbide

Abstract

We present ab initio calculations of the properties of two types of interface between the cubic and hexagonal (wurtzite) polytypes of silicon carbide. The results are derived from density-functional calculations within the local-density approximation and the pseudopotential-plane-wave approach. We first study the interface along the (111) plane (corresponding to (0001) in the hexagonal representation) perpendicular to the stacking axis of the bilayers. Then we consider the interface along the (115) plane, which was already identified experimentally as a grain boundary in silicon and germanium. The (115) interfaces are especially interesting, since they may contribute to a quantum wire consisting of an inclusion of cubic SiC in hexagonal SiC. They are made up of five-and seven-membered atom rings and are free of dangling bonds. The cubic and hexagonal grains are tilted with respect to one another by an angle of 38.94°. In both cases of interfaces, the electronic properties are discussed. Whereas the (111) interface induces practically no states in the bulk fundamental gaps, the particular structure of the (115) interface generates a lot of states, resulting in a metallic behaviour.