Comparative Study of Substrate Type and Post-Annealing Temperature on Thermoelectric Properties of Bi₂Te₃ Thin Films

This study explores the effects of substrate type and post-annealing temperature on the structural and thermoelectric properties of Bi₂Te₃ thin films prepared by DC reactive magnetron sputtering. Films were deposited on both rigid (SiO₂) and flexible (polyimide, PA) substrates, followed by annealing at 50 °C, 150 °C, and 250 °C. Structural characterization via XRD and FE-SEM indicated enhanced crystallinity with increasing temperature, particularly on SiO₂, whereas films on PA exhibited minimal structural evolution due to the substrate's lower thermal stability. EDS analysis showed that annealing shifted the Bi/Te ratio closer to the stoichiometric composition, especially for SiO₂-based films. Thermoelectric measurements revealed that SiO₂-supported films consistently demonstrated lower electrical resistivity, higher Seebeck coefficient, and superior power factor compared to those on PA. The best thermoelectric performance was observed after moderate annealing on SiO₂. These results highlight the critical role of substrate selection and thermal processing in optimizing Bi₂Te₃ thin films for both rigid and flexible thermoelectric device applications.