Sb₂Te₃ and Bi₂Te₃ Thin Films Grown by Room-Temperature MBE

Abstract

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 × 10¹⁹ cm⁻³), large thermopower (130 μV K⁻¹), large charge carrier mobility (402 cm² V⁻¹ s⁻¹), and resulting large power factor (29 μW cm⁻¹ K⁻²). Bi₂Te₃ films also showed low charge carrier density (2.7 × 10¹⁹ cm⁻³), moderate thermopower (−153 μV K⁻¹), but very low charge carrier mobility (80 cm² V⁻¹ s⁻¹), yielding low power factor (8 μW cm⁻¹ K⁻²). The low mobilities were attributed to Bi-rich grain boundary phases identified by analytical energy-filtered TEM.