Thermoelectric properties of bipolar diffusion effect on In₄ Se_3-xTe_x compounds

We present thermoelectric properties and electronic structure of the series compounds of In₄ Se_3-xTe_x (0.0x3.0). Even if the Te-doping is an isoelectronic substitution, we found that the electron dominated carrier transport in Se-rich region (x≤0.2) evolves into the electron-hole bipolar transport properties in Te-rich region (x≥2.5) from the temperature-dependent thermal conductivity κ (T), Seebeck coefficient S (T), and Hall coefficient R_H (T) measurements. The electronic band structures of In₄Se_3-xTe_x (x=0.0, 2.75, and 3.0) are not changed significantly with respect to Te-substitution concentrations. From the Boltzmann transport calculation, the electron-hole bipolar effect on thermoelectric transport properties in Te-rich region can be understood by lowering the chemical potential to the valence band maximum in the Te-rich compounds.