Studying the Optical Properties of CdS Thin Films Prepared by Thermal Vacuum Evaporation Technique with a Different Thickness

CdS thin films with a different thickness have been prepared on glass substrates by using the thermal vacuum evaporation technique at substrate temperature of 150oC. The optical characteristics of the prepared thin films have been investigated by UV-VIS spectrophotometer in the wavelength range (300-1100 nm) . The films have a direct allow electronic transitions and the optical absorption are shifted to the low energies by increasing the thickness . Also the optical energy gap (Eg) has decreased from 2.47 eV to 2.22 eV by increasing the thickness value. The extinction coefficient (k) , refractive index (n) and the real and imaginary dielectric constants (ε1 , ε2 ) are investigated. All of these constants increased with the increases in thickness and shifted to the low energies.