Electronic structure of transition-atom impurities in semiconductors: Substitutional3dimpurities in silicon

The electronic structure of neutral substitutional $3d$ transition-metal impurities in an infinite silicon host crystal has been calculated for the first time. The calculation is carried out self-consistently in the local-density-functional formalism to within a high precision. We use nonlocal, first-principles pseudopotentials and the recently developed quasiband crystal-field (QBCF) Green's-function method. The elements of the electronic structure of this system are discussed in detail. The calculation reveals the chemical trends in the defect energies (gap states as well as resonances) for the impurities Zn, Cu, Ni, Co, Fe, Mn, Cr, V, and Ti, as well as the regularities in the density of states, wave functions, charge distributions, and screening potentials. For charged impurities, the model explains the remarkable occurrence of many charge states in the narrow-band-gap region through a new self-regulating mechanism analogous to the homeostasis control in biological systems.