OPTICAL AND ELECTRICAL INVESTIGATIONS OF N-TYPE BI2SE3 SINGLE-CRYSTALS

Bi2Se3 single crystals were prepared in the electron concentration range from 1.8 x 10(19) to 5.6 x 10(19) cm-3. At room temperature experimental values are given for the specific electrical resistivity, for the Hall and Seebeck coefficients, and the ir-plasma reflectivity spectral were measured in the wave number range from 300 to 4000 cm-1. For the first time it was found that not only the resistivity and the plasma reflectivity but also the thermopower show a distinct anisotropy perpendicular and parallel to the trigonal c-axis, whereas the Hall effect is isotropic. In terms of a one-carrier, one-valley conduction band model with elliptical isoenergy surfaces and a nonparabolic dispersion the anisotropy of the thermopower can be explained in the extrinsic range by an anisotropic mixed scattering mechanism on acoustic phonons and ionized impurities in the relaxation time approximation. In this frame t quantitative, consistent interpretation is reached for all experimental data. The calculated values for the high-frequency dielectric constant. the carrier density, the Fermi level, the parameter of nonparabolicity, the mean optical relaxation times, the effective masses and the drift mobilities are given.