Band Gap Modulation in ZnO Thin Films through Cd Doping by Sol-Gel Method and Its Characterizations

Abstract

Zn1-xCdxO nanocrystalline thin films with different Cd volume ratios (x = 0.00 to 0.35) were successfully deposited by sol-gel spin coating method on p-Si (100) and quartz glass substrates. Thin films were characterized using X-ray diffraction, Atomic force microscopy, UV-Vis spectroscopy and Photoluminescence spectroscopy. XRD results revealed that thin films were polycrystalline in nature and crystallinity reduced with Cd contents. Phase segregation as cubic CdO was observed for x ≥ 0.15. Stress and strain in the films were strongly influenced by Cd contents. The optical reflectance spectra indicated that the optical quality of thin films was degraded with larger cadmium content. The band gap of samples was determined through UV-Vis transmission spectra and it is found that the band gap of ZnCdO thin films decreased exponentially with amount of Cd. Photoluminescence spectra exhibited single near band edge emission in visible violet region for lower Cd contents. This emission surprisingly splits in UV and green- yellow emissions for x ≥ 0.15.