Configuration-interaction energy level diagrams for d7 and d8 charge-state impurities in II-VI and III-V compound semiconductors

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. (C) 1997 Elsevier Science Ltd. All rights reserved.