Electronic structure of the thermoelectric materials Bi2Te3 and Sb2Te3 from first-principles calculations

The electronic structures of Bi2Te3 and Sb2Te3 crystals were calculated using the first-principles full-potential linearized augmented plane-wave method. We studied not only the unrelaxed crystals, which have the experimental lattice parameters and scaled atom coordinates, but also the relaxed crystals, which have the lattice parameters and scaled atom coordinates determined from theoretical structure optimizations. We found that Bi2Te3 has six highest valence-band edges and six lowest conduction-band edges regardless of relaxations. However, by varying structural parameters Sb2Te3 may undergo an electronic topological transition that the number of valence (and conduction) band edges changes between 6 and 12. Moreover, we presented the location of the band edges and the effective mass tenor parameters for electrons and holes associated with those band edges. Furthermore, we discussed the relation of the calculated electronic structures of the two crystals with the electrical properties of Bi2Te3/Sb2Te3 superlattices.