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 i n 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 t hat the local lattice deformation is strongly dependent on the electro nic configuration of impurity atoms, i.e., we find an anomalous expans ion (0.09+/-0.01 Angstrom) along the [111] direction for donor (As) at oms but much smaller magnitude (0.03+/-0.01 Angstrom) for isovalent (G e) atoms and acceptor (Ga) atoms. The results suggest that the local l attice distortions are strongly affected by the Coulomb interactions b etween the localized charge, which piles up to screen the ion core and the bond charge, and the ion-core repulsion. Absence of anomaly in ca se of negatively charged Ga atoms suggests that the former mechanism i s a dominant factor for anomalous lattice expansion. (C) 1997 American Institute of Physics.