Modification of electronic structure and thermoelectric properties of hole-doped tungsten dichalcogenides

We present a study on the modification of the electronic structure and hole-doping effect for the layered dichalcogenide WSe₂ with a multivalley band structure, where Ta is doped on the W site along with a partial substitution of Te for its lighter counterpart Se. By means of band-structure calculations and specific-heat measurements, the introduction of Te is theoretically and experimentally found to change the electronic states in WSe₂. While in WSe₂ the valence-band maximum is located at the Γ point, the introduction of Te raises the bands at the K point with respect to the Γ point. In addition, thermal-transport measurements reveal a smaller thermal conductivity at room temperature of W_1-xTaₓSe1.6Te0.4 than reported for W_1-xTaₓSe₂. However, when approaching 900 K, the thermal conductivities of both systems converge while the resistivity in W_1-xTaₓSe1.6Te0.4 is larger than in W_1-xTaₓSe₂, leading to comparable but slightly smaller values of the figure of merit in W_1-xTaₓSe1.6Te0.4.