Microstructure evolution of sputtered BiSb-Te thermoelectric films during post-annealing and its effects on the thermoelectric properties

This paper reports the results of a study on the microstructure evolution of sputtered BiSb-Te thermoelectric films during post-annealing and its effects on their electronic transport and thermoelectric properties. Combining X-ray diffraction, transmission electron microscopy, and Raman spectroscopy, we illuminate the fundamental aspects of the microstructure evolution: the as-deposited film was Bi_0.5Sb_1.5Te₃ compound in the Bi₂Te₃-type phase with a nano-crystalline microstructure and the post-annealing prompted a drastic grain growth. The electrical and thermoelectric properties also closely changed following the trend of the grain growth. The Seebeck coefficient, electron mobility, and thermal conductivity increase while the carrier concentration remains flat. The ZT value escalates systematically with the annealing time increasing, reaching around 0.94 after 12 h annealing.