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 filmsare investigated. The films are deposited by a flash evaporation method and exhibit apreferred orientation in the c-axis direction. By optimizing deposition conditions, weachieve thin films with clean surfaces. Then, in order to enhance the crystallinity withpreferred orientation and the thermoelectric properties of the thin films, they are annealedin 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 byscanning electron microscopy and x-ray diffraction, respectively. The electricalconductivity, Seebeck coefficient, and thermoelectric power factor are measured at roomtemperature. We confirm that the grain growth and the crystallization along the c-axis areenhanced as the annealing temperature increases. The highest performance of p-typeBi0.4Te3.0Sb1.6 thin films observed in this study have an annealing temperature of 300 oC,resulting in a thermoelectric power factor of 34.9μW cm-1 K-2 at the average grain size of88 nm. We consider that the synthesis conditions reduce the number of potentialscattering sites at grain boundaries and defects, thus improving the thermoelectric powerfactor.