Sb2Te3 and Bi2Te3 thin films grown by room-temperature MBE

Sb2Te3 and Bi2Te3 thin films were grown on SiO2 and BaF2 substrates at room temperature using molecular beam epitaxy. Metallic layers with thicknesses of 0.2 nm were alternately deposited at room temperature, and the films were subsequently annealed at 250°C for 2 h. x-Ray diffraction and energy-filtered transmission electron microscopy (TEM) combined with high-accuracy energy-dispersive x-ray spectrometry revealed stoichiometric films, grain sizes of less than 500 nm, and a texture. High-quality in-plane thermoelectric properties were obtained for Sb2Te3 films at room temperature, i.e., low charge carrier density (2.6 × 10(exp 19) cm-3), large thermopower (130 µV K(exp -1), large charge carrier mobility (402 cm2 V(exp -1) s(exp -1), and resulting large power factor (29 µW cm-1 K(exp -2)). Bi2Te3 films also showed low charge carrier density (2.7 × 10(exp 19) cm-3), moderate thermopower (-153 µV K(exp -1), but very low charge carrier mobility (80 cm2 V(exp -1) s(exp -1)), yielding low power factor (8 µW cm-1 K(exp -2)). The low mobilities were attributed to Bi-rich grain boundary phases identified by analytical energy-filtered TEM.