Influence of induced defects on transport properties of the Bridgman-grown Bi2Se3-based single crystals

Abstract

The impact of induced defects such as Bi intercalants, Bi antisites, and Se vacancies on the transport properties of the Bridgman-grown Bi2Se3-based single crystals in the ab plane were investigated by means of temperature-dependent electrical resistivity, Seebeck coefficient, and thermal conductivity measurements. We found that the Bi2Se3-based crystals can be grown either along the c-axis or perpendicular to it, depending on the different Bi-Se ratios in the starting material. All grown crystals showed a weak metallic behavior with a predominant electron-phonon scattering governing their electrical transport. The absolute value of the Seebeck coefficient of the n-type crystals grown along the c-axis is higher than those grown perpendicular to the c-axis (along the ab plane) at room temperature. The Fermi energy estimated from the Seebeck coefficient data is in the range of 0.20–0.43 eV. The thermal conductivity measurement showed that the lattice phonons dominate thermal transport in these Bi2Se3-based crystals. Analyses of lattice thermal conductivity data of the crystals by the Debye-Callaway approximation revealed that both boundary and point-defect scattering of phonons have a significant effect on the size and shape of the low-temperature phonon peak. These present findings indicate that, in addition to the change in composition, the physical properties of the Bi2Se3-based crystals are also affected significantly by the induced defects. Finally, the near-stoichiometric Bi2.04Se2.99 compound has a room-temperature thermoelectric figure of merit (ZT) of ∼0.12.