In- and cross-plane thermoelectric properties of oriented Bi2Te3 thin films electrodeposited on an insulating substrate for thermoelectric applications

Electrodeposition is a useful technique for preparing Bi2Te3 thin film based thermoelectric generators as power sources for wireless sensors because of its many advantages, including low cost, non-vacuum operation, and compatibility with microfabrication processes. However, electrodeposition of thin films on insulating substrates is challenging; moreover, electrodeposited films exhibit inferior thermoelectric properties. Herein, we report electrodeposition of Bi2Te3 thin films on an insulating substrate by incorporating a sputtering step. The thermoelectric properties of the films were improved by performing post-thermal annealing. A 0.5 µm-thick Bi2Te3 layer was sputter-coated on an alumina substrate; subsequently, Bi2Te3 films of different thicknesses (0.5–3.8 µm) were formed by varying the electrodeposition time (10–60 min). The films were oriented along the a,b-axis direction, while the crystallite size remained constant as the electrodeposition time increased. The thermoelectric properties of the films were evaluated at approximately 300 K in both in- and cross-plane directions. Maximum power factors, 11.0 and 13.9 μW/(cm·K2) in the in-plane and cross-plane directions, respectively, were observed at 60 min electrodeposition due to increased electrical conductivity. The dimensionless figure of merit in both plane directions was maximum (0.27) at 10 min electrodeposition because of low thermal conductivity (0.86 W/(m·K)).