Electronic structure of transition-atom impurities in GaP

We describe the elements of the electronic structure and the chemical trends in cation-substitutional Cr, Mn, Fe, Co, Ni, Cu, and Zn impurities in GaP and Fe in InP. First, using the recently developed method of Fazzio, Caldas, and Zunger, we deconvolute the observed acceptor, donor, and intracenter d→$d^{\mathrm{*}}$ excitation energies into a one-electron mean-field contribution and a many-electron multiplet correction. Then, using the self-consistent quasiband crystal-field Green’s-function method of Lindefelt and Zunger, we show that one-electron theory explains the magnitudes and the trends in the mean-field part of the observed transition energies (evaluated as differences in total energies). Many-electron contributions are found to be sizable, and are responsible for the nonmonotonic trends of the observed acceptor energies with the impurity’s atomic number and a reduction in the Mott-Hubbard Coulomb energies. We discuss in detail the impurity-induced energy levels (gap states as well as resonances), the photoionization and intracenter excitations, the attenuation of the Mott-Hubbard Coulomb repulsion energies with the attendant plurality of charge states, the self-regulating response of the electron density to excitations, and the nature of the transition-atom–host chemical bond with its relationship to the structure of bulk 3d phosphides.