THEORETICAL STUDIES OF THE ATOMIC AND ELECTRONIC STRUCTURES OF GRAIN BOUNDARIES IN SILICON AND SILICON-CARBIDE

Abstract
The atomic and electronic structures of a facetted twin boundary in Si and a twin boundary in β-SiC have been studied theoretically for the first time. The atomic structure of the {211}/{111} facets in Si based on the model by Bourret and Bacmann has been optimised by the Keating model, and the electronic structure has been calculated using a supercell technique and a tight-binding model. It has been found that the distorted region at one of the two types of the facet junctions much influences the electronic structure as compared with the other regions. However, there are no states introduced inside the minimum gap. The atomic and electronic structure of the {122} Σ=9 twin boundary in β-SiC has been calculated using the self-consistent tight-binding method. The calculated boundary energy has shown that the atomic model similar to that in Si or Ge can exist stably in β-SiC, although the Coulomb interaction energy caused by the presence of the wrong bonds is a large part of the boundary energy. The boundary band structure has no deep states in the gap, although the localised states at the wrong bonds have been found at the band edges.