Structural, optical and Urbach energy properties of ITO/CdS and ITO/ZnO/CdS bi-layer thin films

The thin films of ITO/CdS and ITO/ZnO/CdS bi-layer have been fabricated and studied for structural, morphological, optical, and Urbach energy properties. ZnO thin films were coated onto ITO plated glass slides by a spin-coating method and CdS thin films by electron beam evaporation method. X-Ray Diffraction patterns of both ITO/CdS and ITO/ZnO/CdS thin films confirmed the hexagonal wurtzite structure of ZnO and hexagonal structure of CdS, respectively. AFM images show better uniformity and bigger grain size in the case of OTO/ZnO/CdS samples. Optical transmittance spectra show a slight redshift (~ 493 nm to ~ 505 nm) for the film ITO/ZnO/CdS compared to ITO/CdS. Urbach energy was calculated for all the samples to study the structural imperfections leading to the band tails. A decrease in Urbach energy is observed for ITO/ZnO/CdS compared to ITO/CdS. The obtained results indicate that the ITO/ZnO/CdS thin films are more suitable for optoelectronic devices compared to ITO/CdS films. The results obtained are discussed in detail and presented in this paper.