Atomistic modeling of thermoelectric properties of Bi2Te3 and Sb2Te3

Low-dimensional structures with a high density of interfaces exhibit a large thermoelectric figure of merit. For example, a figure of merit ZT=2.5 was measured at 300 K in a Bi$_{2}$Te$_{3}$/Sb$_{2}$Te$_{3}$ superlattice. The design of thermoelectric materials with an even higher figure of merit is conceivable by exploiting the enhancement of the density of states in low dimensionality structures and optimizing the phonon scattering at interfaces to reduce the thermal conductivity. As a step toward modeling such structures, we have computed the thermoelectric properties of bulk Bi$_{2}$Te$_{3}$ and Sb$_{2}$Te$_{3}$ using an atomistic empirical tight-binding method and the Boltzmann transport equation. The tight-binding parameters for the materials are fitted to first-principle band structure calculations. Using the band structures obtained with the tight- binding model and the relaxation time approximation for the scattering, the Seebeck coefficient, the electrical conductivity and the electronic and lattice contribution to the thermal conductivity of bulk Bi$_{2}$Te$_{3} $ and Sb$_{2}$Te$_{3}$ are calculated. The lattice contribution to the thermal conductivity is obtained from a Monte Carlo solution to the Boltzmann equation for phonons.