Configuration-interaction energy level diagrams for d 7 and d 8 charge-state impurities in II–VI and III–V compound semiconductors

Abstract

The so-called configuration-interaction (CI) approach is considered to provide an alternative description of transition metal atoms in solids compared with the conventionally used ligand-field theory which represents a molecular-orbital type approach. To evaluate the potential of the CI approach to describe internal excitations of transition metal impurities in semiconductors, CI energy level diagrams are provided for the d 7 and d 8 charge states in tetrahedral coordination which reveal the explicit energy level dependence on the parameters of the CI approach. The perturbation calculation was restricted to interaction with single-hole configurations of the type |d N + 1 L 〉 where L is a ligand hole. The observed trends in excited-state level energies of cobalt and nickel impurity centres in II–VI and III–V compound semiconductors can well be understood within the CI approach. Though the CI approach does not represent a quantitatively better tool than the classical Tanabe-Sugano approach to describe these transitions occurring at below band-gap energies, it provides a bridge between this more empirical method and the understanding of the influence of covalency on the observed crystal-field splitting and nephelauxetic effect even linking acceptor-type charge-transfer level energies.