Impurity levels of transition metal ions in the crystal field of semiconductors

Abstract

A theory of electron states due to transition metal impurities in semiconductors which includes the real symmetry of the crystal has been developed. The resonance potential, which describes the scattering of valence electrons by excitation of the atomic shell and has the symmetry of the crystal point group, results in the splitting of impurity d-levels and does not affect shallow s-levels. The proposed scheme unites the resonance model of deep levels with conventional ligand field theory which is usually used to explain the optical spectra of wide-gap semiconductors. The possibility of virtual Friedel states in the valence or conduction band and their influence on shallow hydrogen-like impurity levels is also considered.