On the optical study of Pb additive Se-Te-Ge nanocrystalline quaternary alloys

Abstract

In the present study, chalcogenide thin films for different compositions (Se80Te20)94-xGe6Pbx (x = 0, 2, 4 and 6) were prepared by thermal evaporation technique. Optical transmission spectra were taken in the wavelength ranges from 500- 2600 nm. By using the maxima and minima of the interference fringes, optical constants and thickness of the films were derived. Dispersion of refractive index was analyzed using the single-oscillator Wemple and DiDomenico model. Optical band gap (Eg) for non-direct transition was estimated by the Tauc relation. Eg was found to decrease with the increase in lead content. It was found that with the increase in lead concentration, the refractive index (n), absorption coefficient (), extinction coefficient (k), optical conductivity (σ), real (r) and imaginary part (i) of dielectric constant increases. We also compared the value of static refractive index (n0) obtained by WDD (Wemple and DiDomenico) model and by Cauchy's dispersion relation, found that these two values were not in consonance to each other.