ANTI-SITE DEFECTS IN N-BI2SE3 CRYSTALS

The optical properties in the IR region (plasma resonance frequency-omega-p, relaxation time-tau-, high-frequency permittivity-epsilon-infinity) and the transport coefficients (electrical conductivity-sigma-perpendicular-to, Hall constant R(H)(BBAR parallel-to cBAR), Seebeck coefficient-alpha-) of Bi2Se3 single crystals with various contents of incorporated In atoms have been determined. The dependence of the values of omega-p, sigma-perpendicular-to, R(H)(BBAR parallel-to cBAR), alpha of Bi2-x In(x)Se3 crystals on the In-atom concentration x exhibit an extremum near x = 0.1 showing that the free electron concentration increases up to x = 0.1, then decreases. This effect is explained using the idea that anti-site defects exist in the Bi2Se3 crystal lattice. The interaction of In atoms with the anti-site defects leads to the formation of uncharged but positively polarized point defects In(Bi)+delta) and to the decrease of the anti-site defect concentration. The decrease of the anti-site defect concentration is interpreted in the following way: the increasing bond polarity of bonds In(Bi)-Se1 and In(Bi)-Se2 results in the decrease of the probability of anti-site defect formation. Using the experimentally determined dependence of the free-carrier concentration on the x value the energy of anti-site defect formation, E0(Bi'(Se)) = 0.37 eV, has been calculated. The ideas concerning the changes in the bond polarity arising from the increasing content of In atoms have been supported by the quantum chemical calculation of the bonding parameters in Bi(2-x)In(x)Se3 crystals. The physical properties of Bi2Se3 and Bi2Te3 crystals were compared. PACS classification numbers: 61.70.Ey; 61.50.Lt.