First-principles electronic structure and its relation to thermoelectric properties of Bi₂Te₃

The electronic structure of Bi₂Te₃, which is a major constituent of the best thermoelectric material operating at room temperature, was calculated by using the first principles full-potential linearized-augmented-plane-wave method with spin-orbit interaction included by a second variational method. A search of the whole Brillouin zone shows that the band edges are located off the symmetry lines, with locations that are in accord with the phenomenological six-band model. In doped Bi₂Te₃, Fermi surfaces near the band edges show a nonparabolic behavior. At a high doping concentration, the Fermi surfaces display elongated features, i.e., a knifelike Fermi surface for the valence band and spoonlike Fermi surfaces for the conduction band, which can be attributed to the layered structure of Bi₂Te₃. The effect of the anisotropic electronic structure combined with a low lattice thermal conductivity of Bi₂Te₃ gives a large figure of merit.