Studies on the Optical Dispersion Parameters and Electronic Polarizability of Cadmium Sulphide Thin Film
O. Okorie
*
Department of Theoretical Physics, National Mathematical Centre, 904105 Abuja, Nigeria.
A. D. A. Buba
Department of Physics, Faculty of Science, University of Abuja, 900211 Abuja, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Thin film of Cadmium Sulphide (CdS) was deposited onto a precleaned transparent glass substrate by chemical bath deposition technique from a bath containing Cadmium acetate, ammonium acetate, thiourea and ammonium hydroxide. The deposition time was varied from 10 minutes to 50 minutes at an interval of 20 minutes keeping the bath at a constant temperature of using 78HW-1 constant magnetic stirrer. CdS thin film was characterized by UV-Visible spectrophotometer within the wavelength range of 280 nm – 920 nm using Single – Beam Helios Omega UV – VIS spectrophotometer. The optical parameters; extinction coefficient, refractive index and dielectric constant of CdS thin film were analyzed from the absorption spectra and were found to be affected by the deposition time. The optical band gap energy was obtained by Tauc’s equation and were found to decrease from 3.78 eV – 3.70 eV as the deposition time increases. The dispersion parameters (dispersion energy , oscillation energy , moment of optical dispersion spectra and , static dielectric constant and static refractive index ) were calculated using theoretical Wemple-DiDomenico model. The result show that only and behaved differently but other parameters increase as the deposition time increases. The oscillator strength , oscillator wavelength , high frequency dielectric constant and high frequency refractive index were calculated using single Sellmeier oscillator model. While behaved differently other parameters increase as the deposition time increased. Also, Lattice dielectric constant , N/m* and plasma resonance frequency were equally obtained. While decrease with increase in deposition time, N/m* increase with deposition time. The electronic polarizability of CdS thin film was estimated by Lorenz - Lorentz equation and Clausius Mossotti local field polarizability model. The value is an indication that the films showed good response on the application of photon energy. However, its response reduces as the deposition time increases.
Keywords: Dispersion parameter, Wemple-DiDomenico model, single Sellmeier oscillator model, Clausius-Mossotti local field polarizability, CdS thin film