Bi2Te_xSe_y series studied by resistivity and thermopower

TL;DR

This study investigates how resistivity and thermopower vary with temperature and composition in Bi2Te3-xSex, revealing optimal thermoelectric properties near x=0.9 and insights into band structure tuning.

Contribution

It provides detailed experimental data on the composition dependence of resistivity, thermopower, and optical band gap in Bi2Te3-xSex, highlighting the correlation between stoichiometry and electronic properties.

Findings

Resistivity shows a low-temperature plateau in Bi2Te2.1Se0.9.

Thermopower can be modeled as for an extrinsic semiconductor.

Maximum thermopower and band gap occur near x=0.9.

Abstract

We study the detailed temperature and composition dependence of the resistivity, $\rho(T)$, and thermopower, $S(T)$, for a series of layered bismuth chalcogenides Bi$_2$Te$_{3-x}$Se$_x$, and report the stoichiometry dependence of the optical band gap. In the resistivity of the most compensated member, Bi$_2$Te$_{2.1}$Se$_{0.9}$, we find a low-temperature plateau whose onset temperature correlates with the high-temperature activation energy. For the whole series $S(T)$ can be described by a simple model for an extrinsic semiconductor. By substituting Se for Te, the Fermi level is tuned from the valence band into the conduction band. The maximum values of $S(T)$, bulk band gap as well the activation energy in the resistivity are found for $x \approx 0.9$.