Enhanced thermoelectric properties of electrodeposited Bi2Te3 thin films using TiN diffusion barrier layer on a stainless-steel substrate and thermal annealing

Electrodeposition is an efficient wet-chemical approach to reduce the manufacturing cost of thin films. However, the thin films fabricated using this approach show properties inferior to those of the thin films fabricated using dry processes. In this study, a titanium nitride (TiN) diffusion barrier layer was formed on a stainless-steel (SS) substrate to improve the thermoelectric properties of electrodeposited Bi2Te3 thin films. The electrodeposition of the Bi2Te3 films was carried out in the potentiostatic mode using a standard three-electrode cell, followed by thermal annealing at 300-500 degrees C. The X-ray diffraction and electron probe X-ray microanalysis results revealed that impurity diffusion from the SS substrate did not occur in the annealed films deposited on the TiN-coated SS substrate. However, the Bi2Te3-to-Bi4Te5 crystalline phase transformation occurred at higher annealing tem-peratures because of the preferential evaporation of Te atoms from the film surface, leading to the deterioration of the thermoelectric properties of the films. As a result, the 300 degrees C-annealed film formed on the TiN-coated SS substrate showed the highest power factor of 4.4 mu W/(cm.K-2), which is approximately four times higher than that of the corresponding film formed on the bare SS substrate. Therefore, the TiN coating and optimum annealing temperature improved the thermoelectric properties of the electrodeposited Bi2Te3 thin films.