Localized description of the electronic structure of covalent semiconductors. II. Imperfect crystals

Abstract

For pt.I see ibid., vol.8, p.3171 (1975). The localized description of covalent semiconductors is applied to crystals with imperfections, specifically impurity atoms, where the model serves to describe the ground state as well as excitations. Three different impurity systems of substitutional impurity atoms in crystalline silicon are investigated. A sulphur atom yields a donor-type impurity state, formed from a heavily perturbed conduction band state and filled with the two extra p electrons. A zinc atom yields an acceptor-type impurity state, formed from a heavily perturbed valence band state and unfilled due to the lack of two p electrons. An iron atom represents a transition metal impurity, for which the impurity states correspond to antibonding orbitals involving iron 3d contributions. Apart from the impurity state in the band gap, new types of impurity states below the valence band are predicted for the sulphur and zinc impurities. Among discussed effects are the lattice location of the impurity atom, the formation of a localized magnetic moment and Jahn-Teller distortion of the local surrounding of the impurity.