STUDY THE EFFECT OF ANNEALING TEMPERATURE ON OPTICAL PROPERTIESOF CdS THIN FILMS

CdS thin films of thickness 300 nm were deposited on cleaned glass substrates at room temperature (Ts = 250C) by thermal evaporation technique in a vacuum of about 1x 10-5 torr . The films were annealed at a temperature of 2000C for 2 hours in vacuum (10-2 torr). The effect of annealing temperature (Tan) on optical properties was investigated. The optical parameters which were investigated include transmittance, absorbance and reflectance spectra, in addition to optical band gap, refractive index, extinction coefficient, optical conductivity, complex dielectric constant. The optical transmittance, absorbance and optical band gap of films were studied using transmittance measurements which were taken in the spectral region from 400 nm to 900 nm .The as- deposited film was found to exhibit high transmittance, low absorbance in the visible and near infrared regions for wavelength in the range beyond 500 nm to 900 nm. After thermal annealing at 2000C the CdS thin films shows a decrease in the optical transmittance and the optical band gap decreases from 2.50 eV (for as - deposited films) to 2.42 eV ( for annealed films).