High ZT and performance controllable thermoelectric devices based on electrically gated bismuth telluride thin films

High-ZT materials and high-performance devices have always been hot topics in the field of thermoelectric applications. Here we present a field effect transistor (FET) based method to optimize the thermoelectric properties of bismuth telluride thin films, by which Seebeck coefficient, electrical conductivity and carrier type of the films are continuously controllable. As a result, the maximum power factor of the sample reaches 14.9 µWcm^‑1 K^‑2 in N-type and 12.5 µWcm^‑1 K^‑2 in P-type at room temperature. As compared with the bulk, the thermal conductivity of the bismuth telluride thin film is greatly reduced, which is measured to be lower than 0.37 Wm^‑1 K^‑1. The actual ZT of the sample exceeds 1.22 in N-type and 1.02 in P-type at 303 K, respectively. A π-shaped in-plane N-P pair device was built by applying different gate voltage on the bismuth telluride thin films at the two legs, which open circuit voltage is 10.5 mV and the maximum output power is 10.3 nW at a temperature difference of 30 K. By using the Te-doped bismuth telluride thin films, the intrinsic carrier concentration of the sample decreases to 1.05 × 10¹⁷/cm³ (N-type) and the films can be tuned into N-type and P-type by the opposite gate voltage symmetrically. Using this material, a thin film thermocouple with a quasi-linearly adjustable sensitivity from 2.4 to 225.5 µVK^‑1 by voltage was obtained. This work provides a general method to obtain high-ZT of thermoelectric materials and new ideas for fabricating performance controllable device with the same thermoelectric material, which greatly simplifies the material growth process in device manufacturing.