Investigation on Thickness Dependent Structural, Optical and Electrical Properties of Cadmium Selenide Thin Films Deposited via Thermal Process

Nanocrystalline CdSe thin films of various thicknesses have been deposited on cleaned glass substrates using thermal vacuum evaporation technique at substrate temperature of 333K. The effect of thickness on the structural, optical, dielectric, and electrical properties of CdSe thin films has been studied. Structural studies using an X-ray diffractometer (XRD) reveal that the deposited samples are polycrystalline. Optical investigation using ultraviolet visible (UV-Vis) spectroscopy shows that the films exhibit direct allowed electronic transitions, and the optical absorptions are found to shift towards lower energies with increasing thickness. The optical energy band gap (Eg) decreases from 2.36 eV to 2.12 eV as the sample thickness increases, attributed to the rise in the grain size of the CdSe nanoparticles. The fundamental dielectric constant decreases with an increase in film thickness, and the imaginary dielectric constant increases with increase in film thickness. The increase of photonic energy increases both real and imaginary dielectric constants. External illuminating radiation generates photocarriers that interact with the grain boundary state and reduce potential barrier.