Optimized thermoelectric performance of Bi2Te3 nanowires

The structural and electronic properties of a series of stoichiometric Bi2Te3 nanowires with two growth orientations [110] and [210] are studied by using density functional calculations. Our results indicate that the nanowires with [110] orientation are energetically more favorable than those with [210] orientation. All the investigated Bi2Te3 nanowires are found to be semiconducting and the band gaps of [110] nanowires monotonically increase with the decreasing cross-sectional width. For the [210] orientation, however, the band gaps exhibit an interesting width-dependent even-odd oscillation behavior. The electronic transport properties of these nanowires are then evaluated by using the semiclassical Boltzmann theory with the relaxation time approximation. For the phonon transport, the lattice thermal conductivity is predicted by using the non-equilibrium molecule dynamics simulations. Our theoretical calculations suggest that the thermoelectric performance of Bi2Te3 nanowires can be optimized at appropriate carrier concentration with particular orientation and cross-sectional size. The figure of merit (ZT value) can reach as high as 2.3 at 300 K and 2.5 at 350 K for the [210] nanowire with the width N = 5.