Local Structure of dilute impurities in Si crystal by fluorence XAFS

Local structures of dilute isovalent and heterovalent impurity atoms in Si crystal (Si:X, X=Ga, Ge, As) have been studied by fluorescence XAFS. The results indicate that the local lattice deformation is strongly dependent on the electronic configuration of impurity atoms. The As-Si bond length is 0.244 nm while both Ge-Si and Ga-Si bond lengths are 0.238 nm, We find an anomalous expansion (0.009 nm) along the [111] direction for donor (As) atoms but much smaller magnitude (0.003 nm) for isovalent (Ge) atoms and acceptor (Ga) atoms. An electronic charge density is piled up to screen the ion core is a dominant factor for anomalous lattice expansion.