RSM Base Study of the Effect of Argon Gas Flow Rate and Annealing Temperature on the [Bi]:[Te] Ratio and Thermoelectric Properties of Flexible Bi-Te Thin Film

Abstract

Bismuth telluride (Bi-Te) thin films coated on a flexible substrate were prepared by RF (radio frequency) magnetron sputtering technique. A response surface methodology based on a central composite design was used to optimize deposition parameters, including the amount of Ar gas flow rate (100.5–106.5 sccm) in the sputtering process and the annealing temperature (250–320°C) for stoichiometric Bi₂Te₃ thin films. The mathematical model was validated and proven to be statistically sufficient and accurate in predicting a response (Te content). The stoichiometric Bi₂Te₃ thin films can be prepared on terms appropriate to the Ar flow rate and annealing temperature under several conditions, such as at the Ar flow rate of 103.5 sccm followed by an annealing temperature of 285°C. The characterization of the crystal structure and surface morphology of selected samples with different [Bi]:[Te] content were analyzed by x-ray diffraction (XRD) and a field emission scanning electron microscope, respectively. The XRD spectra showed Bi-Te and Bi₂Te₃ structures that corresponded with the ratio of [Bi]:[Te]. The Seebeck coefficient and electrical conductivity were simultaneously measured at room temperature and up to 300°C by a direct current four-terminal method. The maximum power factor of the stoichiometric Bi₂Te₃ thin film was 61×10⁻⁵ W/K²m at 243°C.