Structural and thermoelectric properties of fine-grained Bi0.4Te3.0Sb1.6 thin films with preferred orientation deposited by flash evaporation method

Structural and thermoelectric properties of p-type fine-grained Bi0.4Te3.0Sb1.6 thin films are investigated. The films are deposited by a flash evaporation method and exhibit a preferred orientation in the c-axis direction. By optimizing deposition conditions, we achieve thin films with clean surfaces. Then, in order to enhance the crystallinity with preferred orientation and the thermoelectric properties of the thin films, they are annealed in hydrogen ambient at atmospheric pressure and temperatures ranging from 200 to 350 oC. The cross-sectional microstructure and crystallinity of the thin films are investigated by scanning electron microscopy and x-ray diffraction, respectively. The electrical conductivity, Seebeck coefficient, and thermoelectric power factor are measured at room temperature. We confirm that the grain growth and the crystallization along the c-axis are enhanced as the annealing temperature increases. The highest performance of p-type Bi0.4Te3.0Sb1.6 thin films observed in this study have an annealing temperature of 300 oC, resulting in a thermoelectric power factor of 34.9 W cm-1 K-2 at the average grain size of 88 nm. We consider that the synthesis conditions reduce the number of potential scattering sites at grain boundaries and defects, thus improving the thermoelectric power factor