Effect of Se content on the structural, morphological and optical properties of Bi2Te3−ySey thin films electrodeposited by under potential deposition technique

Abstract

Bi2Te3−ySey thin films with different Se contents ranging from 0.3 to 2.5 were successfully electrodeposited by under potential deposition (UPD) technique onto gold foil substrates from an electrolyte consist of Bi(NO3)3, TeO2, and SeO2 at ambient conditions. The effects of Se content on structural, morphological and optical properties of the products were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and FT-IR spectroscopy, respectively. The XRD analysis revealed that the diffraction peaks positions of Bi2Te3−ySey thin films shifts gradually towards the higher angle side due to replacement of Te by Se atoms in the crystal structure with increasing Se content. The SEM results showed that the particle size of Bi2Te3−ySey thin films decreased as the Se content increased. The optical constants of ternary Bi2Te3−ySey thin films such as refractive index, extinction coefficient, and dielectric constant were obtained from the transmission spectra in the range of 2500–10.000nm. The direct allowed band gap energies were estimated using Tauc equation and found to increase from 0.210 to 0.282eV with increasing Se content from 0.3 to 2.5. The dispersion behavior of refractive index was studied by the single oscillator Wemple-DiDomenico model.