Local structures of isovalent and heterovalent dilute impurities in Si crystal probed by fluorescence x-ray absorption fine structure

Local structures of dilute isovalent and heterovalent impurity atoms in Si crystal (Si:X, X=Ga, Ge, As) have been studied by fluorescence x-ray absorption fine structure. The distortion of local lattice around the impurity atoms was evaluated from the Si-X bond length determined by extended x-ray absorption fine structure. The results demonstrate that the local lattice deformation is strongly dependent on the electronic configuration of impurity atoms, i.e., we find an anomalous expansion (0.09+/-0.01 Angstrom) along the [111] direction for donor (As) atoms but much smaller magnitude (0.03+/-0.01 Angstrom) for isovalent (Ge) atoms and acceptor (Ga) atoms. The results suggest that the local lattice distortions are strongly affected by the Coulomb interactions between the localized charge, which piles up to screen the ion core and the bond charge, and the ion-core repulsion. Absence of anomaly in case of negatively charged Ga atoms suggests that the former mechanism is a dominant factor for anomalous lattice expansion.