Localized defect states in tetrahedrally bonded semiconductors

A simple tight-binding model is presented for interstitial and substitutional defects in tetrahedrally bonded semiconductors with significant ionic and metallic character. The small cluster surrounding the defect is separated from the rest of the crystal without breaking any covalent bonds, and while preserving the correct charge transfer at the boundary. Estimates of total defect energies, energies of localized defect levels, and the symmetry and orbital composition of the localized states are obtained. Results of this method are compared with experimental and self-consistent Green's function results for Si, GaAs, GaP, and CdTe. (author) 19 refs., 1 fig., 3 tabs