Thermoelectric properties of bismuth telluride nanowires in the constant relaxation-time approximation

Abstract

Electronic structure of bismuth telluride nanowires with the growth directions [110] and [015] is studied in the framework of the anisotropic effective mass method using the parabolic band approximation. The components of the electron and hole effective mass tensors for six valleys are calculated for both growth directions. For a square nanowire, in the temperature range from 77 K to 500 K, the dependence of the Seebeck coefficient S, the thermal κ and electrical conductivity σ as well as the figure of merit ZT on the nanowire thickness and on the excess hole concentration pex are investigated in the constant-relaxation-time approximation. The carrier confinement is shown to play essential role for nanowires with cross section less than 30 × 30 nm 2 . In contrast to the excess holes (impurities), the confinement decreases both the carrier concentration and the thermal conductivity but increases the maximum value of the Seebeck coefficient. The confinement effect is stronger for the direction [015] than for the direction [110] due to the carrier mass difference for these directions. In the restricted temperature range, the size quantum limit is valid when the p−type nanowire cross section is smaller than 8 × 10 nm 2 (6 × 7 nm 2 and 5 × 5 nm 2 ) at the excess hole concentration pex = 2 × 10 18 cm −3 (pex = 5 × 10 18 cm −3 and pex = 1 × 10 19 cm −3 correspondingly). The carrier confinement increases the maximum value of ZT and shifts it towards high temperatures. For the growth direction [110], the maximum value of the figure of merit for the p−type nanowire is equal to 1.4, 1.6, and 2.8, correspondingly, at temperatures 310 K, 390 K, and 480 K and the cross sections 30 × 30 nm 2 , 15 × 15 nm 2 , and 7 × 7 nm 2 (pex = 5 × 10 18 cm −3 ). At the room temperature, the figure of merit equals 1.2, 1.3, and 1.7, respectively.

Thermoelectric properties of indium-filled InxRh4Sb12 skutterudites

“…Single-crystal studies have reported an even larger hole mobility (8 × 10 3 cm 2 V −1 s −1 ) in unfilled Rh 4 Sb 12 [23]. In contrast, the hole and electron mobility ratios in intrinsic Bi 2 Te 3 and Si, both known to show appreciable bipolar thermal diffusion, are one to two orders of magnitude less than the skutterudites [21,24,25]. Therefore, it is likely that a vast disparity in hole and electron mobility in completely intrinsic Rh 4 Sb 12 prohibits appreciable bipolar thermal diffusion as only one charge carrier (holes) likely dominates the electrical conductivity (Eq.…”

Molecular Dynamics Simulation of Mechanical Properties of Single-Crystal Bismuth Telluride Nanowire

“…In recent years, various methods have been applied to synthesize nanostructured thermoelectric materials, [3][4][5][6] and extensive experimental work has been performed with particular focus on their electronic and thermal properties. [7][8][9] However, the mechanical properties of such nanowires are not known in detail. The immense potential of Bi 2 Te 3 nanowires has called for research into their mechanical properties.…”

Atomistic calculation of the thermoelectric properties of Si nanowires

“…The effective mass approximation and the k.p theory were widely used for transport calculations. [7][8][9][10] These approaches become questionable for nanowires, at least if their diameter is just a few lattice constants. Atomistic methods, such as the tight-binding (TB) electronic structure approach or density functional theory calculations, should be used instead.…”