Optimization of annealing conditions to enhance thermoelectric performance of electrodeposited p-type BiSbTe thin films

Swatchith Lal,Devendraprakash Gautam,Kafil M Razeeb

doi:10.1063/1.5049586

Abstract

In this work, we report the optimization of annealing process to improve the thermoelectric properties of pulse electrodeposited bismuth antimony telluride (Bi–Sb–Te) films by varying the annealing time-temperature profile. The innovative approach of sandwiched Te in between the Bi–Sb–Te layers aids in compensating the loss of tellurium during the annealing of BiSbTe thin films. An optimized Seebeck coefficient of 90.5 µV/K along with a power factor of 240 µW/mK2 is achieved for samples annealed at 350 °C for 1 h under N2 atmosphere with controlled heating and cooling rates. These improvements are attributed to a significant decrease in the carrier concentration as substantiated by the Hall measurements and to the increase in the crystallite size at the elevated temperatures as indicated by the X-ray diffraction pattern data. A comprehensive study on the annealing parameters reveals that the Seebeck coefficient and the electrical conductivity are considerably more sensitive to the annealing temperature than compared to the annealing time.

Highlights

It can be seen that a decrease in the carrier concentration increases the Seebeck coefficient and decreases the electrical conductivity
One of the significant problems associated with the annealing of bismuth telluride alloy thin films is the evaporation of tellurium (Te) at elevated temperatures due to its high vapour pressure and thereby impacting on the composition and the TE properties of thin films
Building-up on our previous work of using an encapsulated Te layer between the p-type BiSbTe film,16 here we study the effect of annealing parameters on the TE properties of electrodeposited p-type BiSbTe films

Summary

Introduction

Where m∗ is the effective mass, kb is the Boltzmann constant, e is the electron charge, h is the Planck constant, n is the charge carrier concentration, μ is the mobility of charge carrier, ρ is the electrical resistivity, and T is the absolute temperature.1 From the above relation, it can be seen that a decrease in the carrier concentration increases the Seebeck coefficient and decreases the electrical conductivity. The thermal treatment of the electrodeposited films was performed under the controlled flow of N2 atmosphere in a rapid thermal annealing (RTA) system for a different time duration ranging from 15 min to 1 h and at different scitation.org/journal/apm temperatures ranging from 250–400 ◦C.

Results

Conclusion