STUDY THE OPTICAL PROPERTIES OF CdS THIN FILMS PREPARED BY THERMAL EVAPORATION TECHNIQUE

Cadmium Sulfide (CdS) thin films with different thickness, 100, 200 and 300 nm, are deposited onto glass substrates by thermal evaporation technique. The effect of films thickness on optical properties is investigated. The optical parameters investigated include transmittance, absorbance, and reflectance spectra, in addition to optical band gap, refractive index, extinction coefficient, optical conductivity and complex dielectric constant. It is found that the optical parameters depend on the film thickness. The absorption coefficient and optical band gap energy of films at the fundamental absorption region are determined using the spectral data of transmittance measurements within the wavelength range 350 - 900 nm. It is foun dalso that the optical band gap decreases from 2.75 – 2.65 eV when the films thickness increases from 100 nm to 300 nm. All the films are found to exhibit high transmittance (78-99%), while low absorbance and low reflectance in the visible and near infrared region up to 900 nm.