(Invited) Effect of Annealing on Thermoelectric Properties of Electrodeposited Bisbte Films
Authors: Lal Swatchith , Gautam Devendraprakash , Razeeb Kafil M. 
Published: February 2020

Thermal management of microelectronics and optoelectronics devices using thermoelectric (TE) coolers is an efficient way for active temperature control, where miniaturization of the devices led to generate a high heat flux, which is difficult to manage1, 2. In this regard, bismuth telluride (Bi-Te) based materials have been extensively studied due to their relatively high thermoelectric efficiency near room temperature regime for the fabrication of thermoelectric devices. Various deposition techniques have been used for the growth of Bi-Te thin films such as sputtering3, metal organic chemical-vapor deposition4, molecular beam epitaxy 5 and electrodeposition6. The use of electrodeposition in synthesis of thermoelectric materials and device is highly recommended due to its suitability in terms of cost effectiveness, up-scalability and ease of controlling material properties such as composition, crystallinity and morphology. Moreover, because of its compatibility with microelectronic processing techniques, electrodeposition can be used to fabricate micro-scale thermoelectric cooler directly on the wafer for thermal management of photonics and electronic devices. But the thermoelectric efficiency of these electrodeposited films is still low.

Thermal annealing of electrodeposited film is one of the ways to enhance the TE properties7. The effect of annealing has been examined for different types of thermoelectric films fabricated using different deposition techniques7-9. However, a systematic study of annealing parameters on the electrodeposited p-type BiSbTe film is still missing. Thereby, in this work we have investigated the effect of annealing parameters in enhancing the TE properties of electrodeposited p-type BiSbTe films. The influence of thermal annealing on microstructure and TE properties were investigate within a temperature range of 250 - 400 °C in nitrogen atmosphere. Scanning electron microscopy (Figure 1) and x-ray diffraction techniques were used to study the change in microstructure and crystallinity of the films. Seebeck coefficient and electrical conductivity were measured at room temperature. It was observed that increasing the annealing temperature increased the Seebeck coefficient. A maximum Seebeck coefficient of 94 μV/K and a corresponding power factor of 263.72 µW/mK2 was obtained for the p-type BiSbTe film annealed at 350 °C for 1h. We found that the annealing parameters played a vital role in determining the thermoelectric (TE) properties of the film. Further increase in the annealing temperature led to a decrease in the TE properties due to the depletion of tellurium content in the films. The influence of the annealing parameters on the TE properties for the p-type BiSbTe based electrodeposited films were analyzed in detail with a view to fabricate a complete thermoelectric device.

Acknowledgment

Authors acknowledge financial support from the European Union’s Horizon2020 funded project “Thermally Integrated Smart Photonics Systems (TIPS)”, under the grant agreement No. 644453. This publication has emanated from research supported in part by a research grant from Science Foundation Ireland (SFI) and is co-funded under the European Regional Development Fund under Grant Number 13/RC/2077.

Corresponding author's email addresses: kafil.mahmood@tyndall.ie

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Figure 1. SEM image of electrodeposited BiSbTe films annealed at different temperatures for 1 hour.

Figure 1