Effect of deposition temperature on the structural and thermoelectric properties of bismuth telluride thin films grown by co-sputtering

Thermoelectric bismuth telluride thin films were prepared on SiO2/Si substrates by radio-frequency (RF) magnetron sputtering. Co-sputtering method with Bi and Te targets was adopted to control films' composition. BixTey thin films were elaborated at various deposition temperatures with fixed RF powers, which yielded the stoichiometric Bi2Te3 film deposition without intentional substrate heating. The effects of deposition temperature on surface morphology, crystallinity and electrical transport properties were investigated. Hexagonal crystallites were clearly visible at the surface of films deposited above 290 °C. Change of dominant phase from rhombohedral Bi2Te3 to hexagonal BiTe was confirmed with X-ray diffraction analyses. Seebeck coefficients of all samples have negative value, indicating the prepared BixTey films are n-type conduction. Optimum of Seebeck coefficient and power factor were obtained at the deposition temperature of 225 °C (about − 55 μV/K and 3 × 10− 4 W/K2·m, respectively). Deterioration of thermoelectric properties at higher temperature could be explained with Te deficiency and resultant BiTe phase evolution due to the evaporation of Te elements from the film surface.