Size quantization and thermoelectric properties of bismuth telluride nanowires

Electronic structure of bismuth telluride quantum wires with growth directions [110] and [015] is studied in the framework of anisotropic effective mass method using parabolic band approximation. The components of the electron and hole effective mass tensor for six valleys are calculated for both growth directions. In the temperature range from 77 K to 500 K, the dependence of the quantum wire Seebeck coefficient, S, electron thermal, kappa, and electrical, sigma, conductivity as well as figure of merit, ZT, on the square quantum wire thickness and excess hole concentration, pex, are investigated in constant relaxation time approximation. For p-type Bi2Te3 quantum wires, the maximum value of the figure of merit is equal to 1.4; 1.6; and 2.8 at the corresponding temperatures 310 K; 390 K; 480 K and quantum wire thickness 30 nm; 15 nm, and 7 nm (pex=5times1018 cm-3).