Core structure and electronic bands of the 90° partial dislocation in silicon

Abstract

The core structure of the 90° partial dislocation in silicon is obtained by energy minimization of a cluster with respect to a Lifson-Warshel valence force field. Both the reconstructed and unreconstructed topologies are considered, and the reconstructed structure is favoured by 2·66 eV per lattice vector. Comparison of these structures with the one resulting from the anisotropic elastic approximation shows that the latter introduces a spurious bond length alternation. Electronic dislocation bands are determined by the extended Hückel theory, the parameters of which are obtained by calculation and fitting of the perfect silicon lattice. For the reconstructed structure, the lower dislocation band dips by more than 1 eV below the top of the valence band (E _v) and the upper band—unoccupied, of width 1·2 eV—lies in the gap, extending from about 0·4eV above E _v until it overlaps the bottom of the conduction band. Comparison of the bands for the elastic and unreconstructed structures indicates that the spurious bond length alternation of the elastic structure pulls the lower dislocation band over E _v.