Thermoelectric transport and magnetoresistance of electrochemical deposited Bi2Te3 films at micrometer thickness

Abstract

Bismuth telluride (Bi2Te3) is so far the best thermoelectric material for applications near room temperature, and also exhibits large magnetoresistance. While the electrochemical deposition approach can achieve effective growth of the Bi2Te3 films at micrometer thickness, the magnetoresistance transportation behavior of the electrochemically deposited Bi2Te3 films is yet not clear. In this work, we demonstrate the thermoelectric and magnetoresistance behaviors of the micrometer thick Bi2Te3 films deposited via electrochemical deposition approach. The optimum thermoelectric power factor is observed in the Bi2Te3 sample with electrochemical deposition thickness of ~6 μm followed by rapid photon annealing treatment, reaching the magnitude of ~1 μWcm−1K−2 that is similar to the previous reports. In contrast to the single crystalline or vacuum deposited Bi2Te3 or Bi2Se3 films, the electronic transportations of the electrochemically deposited Bi2Te3 are more influenced by the carrier scatterings by the grain boundaries and lattice defect. As a result, their magnetoresistance (MR) shows a distinguished non-monotonic behavior when varying the magnetic field, while the magnitude of their MR exhibits a positive temperature dependence. These MR behaviors largely differ to the previously reported ones from the single crystalline or vacuum deposited Bi2Te3 or Bi2Se3, in which cases their MR monotonically increases with the magnetic field and exhibits negative temperature dependence. This work reveals the previously overlooked role of grain boundary that also regulates the transportation properties of bismuth chalcogenides in the presence of magnetic field.