Effect of thermal annealing on thermoelectric properties of Bi_xSb_(2-x)Te_3 thin films grown by sputtering

摘要

The present study focuses on the enhancement of the Seebeck coefficient (S) of BiSbTe alloy thin films on post-deposition annealing. It is demonstrated that thermal treatment leads to about twofold enhancement in the S of BiSbTe alloy thin films deposited using DC magnetron sputtering. Investigation of the enhanced thermoelectric properties has been done by studying their phase, compositional, and structural properties. The x-ray diffraction patterns show the presence of a mixed Bi_xSb_(2-x)Te_3 phase, which crystallizes in the Sb-rich phase on annealing. The surface morphology of the as-deposited samples exhibit spherical features that grow in the form of hexagonal rods on increasing the annealing temperature to 300 °C. However, on further increasing the annealing time to 3 h at 300 °C, distorted cubical micro-structures were observed. The microstructures had a higher Sb/Bi ratio, implying that these structures were Sb rich. The thermoelectric properties of the nanostructured Bi_xSb_(2- x)Te_3 films were studied as a function of annealing temperature and time. An enhancement of about two orders of magnitude is observed both in the S and power factor for the samples annealed at 300 °C for 3 h. This enhancement is attributed to the energy filtering of charge carriers at the junction of the Bi_xSb_(2-x)Te_3 matrix and Sb-rich inclusions. These results indicate that annealing is an efficient way of tuning the growth of microstructures and the S of Bi_xSb_(2-x)Te_3 thin films.