Investigation of the thermoelectric properties of Bi2Te3 thin films by thermal evaporation processes

• Main Authors: Chi-Pi Lin, 林祺弼
• Other Authors: Ying-Chung Chen
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/ad39e2

碩士 === 國立中山大學 === 電機工程學系研究所 === 102 === The energy sources, such as petroleum, coal, coal gas, etc., will exhaust in the near future. On the other hand, the thermoelectric power generator exhibits the advantages of environmental protection and renewable energy. It generates electric energy from the useless heat by thermoelectric effect. Bismuth telluride based compounds is the best thermoelectric materials in the room temperature. In this study, thermal evaporation processes were adopted to fabricate the n-type Bi2Te3 thin films. The influences of substrate temperature and annealing temperature on the surface morphology, crystal structure and thermoelectric properties of the films were investigated. Further, the Ag-doped Bi2Te3 thin films were fabricated by co-evaporation, and their properties were compared with those of undoped Bi2Te3 thin films. For the undoped Bi2Te3 thin films, when the substrate temperature increased, the grain size of thin film whi observed by SEM also increased. Furthermore, from the analysis of X-ray diffraction patterns, the crystallization of Bi2Te3 thin films would be optimized at substrate temperature of 150°C. But when the temperature reaches 200°C, the BiTe phase existed and the quality of thin film was deteriorated. In addition, it caused the thin film changed from n-type to p-type and the Seebeck coefficient increased at first then decreased. The maximum value of power factor was 4.89 µW/cm∙K2 at the substrate temperature of 150°C. After thermal annealing, the crystalline structure of the thin film was improvd and the number of defects was decreased, the Seebeck coefficient would increase. The maximized value of power factor (6.05 µW/cm∙K2) could be obtained at the substrate temperature of 150°C, and annealing temperature of 250°C (0.5hr) . Finally, the doping of Ag was adopted to modulate the Seebeck coefficient and the electrical conductivity. The maximized value of the power factor (2.1 µW/cm∙K2) could be obtained at the doping concentration of 16.7wt%, the substrate temperature of 150°C, and the annealing temperature of 100°C (0.5hr).