Effect of Annealing Temperature on the Thermoelectric Properties of the Bi_0.5Sb_1.5Te₃ Thin Films Prepared by Radio-Frequency Sputtering

The effect of annealing temperature on the crystallinity, thermoelectric properties, and surface morphology of the Bi_0.5Sb_1.5Te₃ thin films prepared on SiO₂/Si substrate by radio-frequency (RF) magnetron sputtering was investigated using X-ray diffraction (XRD), the four-point probe method, and scanning electron microscopy (SEM). XRD results show that the crystallite structure of the Bi _x Sb_2–x Te₃ thin films belong to Bi_0.5Sb_1.5Te₃. When the Bi _x Sb_2–x Te₃ thin films were annealed between 423 K and 523 K (150 °C and 250 °C) for 10  minutes, the crystallinity of the thin films continuously increases with the temperature increase. In addition, the (015) reflection plane as the preferred orientation and the oxidation compound of Bi_3.73Sb_1.5O₃ first appeared when the Bi_0.5Sb_1.5Te₃ thin films were annealed at 523 K (250 °C) for 10 minutes. An activation energy of 51.66 kJ/mol for crystallite growth of Bi_0.5Sb_1.5Te₃ thin films annealed between 423 K and 523 K (150 °C and 250 °C) for 10 minutes was obtained. The resistivity was 2.69 × 10² and 5.93 × 10  μΩ·m, respectively, for the as-deposited Bi_0.5Sb_1.5Te₃ thin films and annealed at 523 K (250 °C) for 10 minutes. The maximum values of the Seebeck coefficient and power factor were 256.5 μV/K and 1.12 × 10³ μW/m·K², respectively, for the Bi_0.5Sb_1.5Te₃ thin films annealing treatment at 523 K (250 °C) for 10 minutes.