Hyperfine Interaction of the Iron Impurity Nuclei at the Tetrahedral Interstitial Site in Silicon

Abstract

Most electronic structure calculations on transition metal impurities in semiconductor1–6 were performed within the local density formalism7, implemented either in an extended-crystal Green’s function approach1–2, or within finite cluster models3–6. Involving a local (statistical) approximation to exchange and correlation, the local density approximation, much like its predecessor, the Thomas-Fermi model involves an un-physical interaction of each spin-orbital with itself8 (self-interaction). Whereas this interaction has a vanishing effect on extended delocalized states, it may have a significant effect on localized states. Such is the case for isolated transitionatoms, where a self-interaction corrected model shows8 that relative to LSD (i) the 3d orbitals move to substantially more negative energies (increasing thereby the s-d separation), (ii) the 3d orbitals become more localized, whereas the non-d (valence) orbitals become more expanded, (iii) the exchange splitting between spin-up and spin- down 3d orbitals increases, (iv) the contact spin density at the nucleus is reduced, (v) the total exchange energy becomes more negative, whereas the total correlation energy becomes less negative, and (vi) the total ground state density becomes more localized. Whereas self-interaction corrections (SIC) were applied recently with great success to atoms,8 molecules9 and solids8,10, showing substantial improvements relative to the uncorrected formalism, until recently11 they were not considered for impurities. Of particular interest here are the interstitial 3d impurities that are likely to maintain their localized atomic-like characteristics more than the substitutional impurities, (the former have only weak bonds with the chemically saturated host ligand atoms). Following the recent demonstration11 of the significance of the SIC to such systems (treated perturbutively), we have undertaken here a self-consistent SIC study of Si:Fe.12