ICT2014 Abstracts

Bi_2-xSb_xTe₃-based materials are the state-of-the-art thermoelectrics for operations at around room temperature. Grown as thin films with the preferred crystal orientation (00l), they exhibit excellent electrical properties. In this research, we report on the epitaxial growth of Bi_2-xSb_xTe₃ (0≤x≤2) thin films on the sapphire (0001)-oriented substrates using the Molecular Beam Epitaxial (MBE) technique and we discuss the electrical properties of such films as a function of the Bi/Sb ratio. In-situ Reflection High Energy Electron Diffraction (RHEED) analysis combined with X-ray diffraction measurements reveal the layer-by-layer growth of Bi_2-xSb_xTe₃ films during the deposition process and their (00l) orientation. Electronic transport measurements indicate a p-n transition in the Bi_2-xSb_xTe₃ films for concentrations between x=1.4 and 1.3 due to a competition between the positively charged and negatively charged point defects in Sb₂Te₃ and Bi₂Te₃, respectively. The power factor of Bi_2-xSb_xTe₃ films first decreases and then increases with increasing the Sb content, while the lowest value is obtained near the composition with p-n transition. High power factor of 4.97 and 1.81 mWm^-1K^-2 are achieved separately for Bi₂Te₃ and Sb₂Te₃ in our research. Further enhancements in the power factor of Bi_2-xSb_xTe₃ films are expected to come from tuning the carrier density via annealing and doping.

The work is supported by the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award DE-SC0000957.