Composition-dependent characterization and optimal control of electrodeposited Bi2Te3 films for thermoelectric application

A method to control composition of Bi2Te3 films by mass transfer manipulation has been developed. The film composition can be varied by a diffusion-controlled method, which is related to the change of Bi3+/HTeO2+ ratios in a controlled diffusion layer. A homogeneous and dense film with precise chemical composition could thus be obtained under constant electrode polarization. Meanwhile, the solo dependence of film properties on composition change of both Te-rich and Bi-rich films were investigated. Firstly, the studies of XRD and FE-SEM showed that different Te contents in deposit would lead to different dimensions of unit cell and grain sizes. The Seebeck coefficient increased apparently when the Te content was over 60 at.% Te. Te-rich films had higher carrier concentration but slower mobility than Bi-rich films. Inverse relations were observed between carrier concentration and carrier mobility and between Seebeck coefficient and conductivity. Therefore, an optimal power factor of 7 × 10−4 W/m K2 was realized near the stoichiometric Bi2Te3.