BI2TE3 CRYSTALS HEAVILY DOPED WITH TIN ATOMS

The values of transport coefficients (Hall constant and Seebeck coefficient) of Bi2Te3 crystals strongly doped with Sn atoms are determined at room temperature. From reflectivity measurements in the IR region, the plasma resonance frequency omega-p, relaxation time tau, and high frequency permittivity are found. The interpretation of the results obtained in the concentration interval, 0 < x < 3 x 10(20) Sn atoms per cm3, leads to the conclusion that one part of the Sn atoms incorporated enters into the bismuth sublattice giving rise to negatively charged substitutional defects Sn'(Bi), the other part forms uncharged defects. The formation of uncharged defects produced by the incorporation of Sn-atoms into the Bi2Te3 crystal lattice is explained in the following way: Sn-atoms form seven-layer-lamellae of the composition Te-Bi-Te-Sn-Te-Bi-Te which corresponds to the structure of the SnBi2Te4 compound; this seven-layer-lamella is uncharged. The formation of such a seven-layer-lamella can easily explain the experimental results: Sn-atoms incorporated into the seven-layer-lamella are electrically inactive.