Experimental investigation and comparative analysis of electron beam evaporated ZnO/MgxZn1-xO/CdxZn1-xO thin films for photodiode applications

Abstract

— This work reports the growth optimization and analysis of ZnO, Mg<inf>x</inf>Zn<inf>1-x</inf>O, and Cd<inf>x</inf>Zn<inf>1-x</inf>O thin films on silicon substrate using an electron beam evaporation system. The crystal phase purity, surface morphology, optical and electrical properties of deposited ZnO, Mg<inf>x</inf>Zn<inf>1-x</inf>O, and Cd<inf>x</inf>Zn<inf>1-x</inf>O thin films were studied. X-ray diffraction (XRD) spectra revealed that the deposited films were polycrystalline in nature with preferred (002) crystal orientation. Field emission scanning electron microscope study showed a dense-packed grained structure with an exact symmetrical distribution. The root-mean-square roughness of 3.03 nm was perceived by atomic force microscopy measurement for Mg<inf>x</inf>Zn<inf>1-x</inf>O thin-film, indicating good morphology of the deposited film. Photoluminescence measurement demonstrated a near-band-edge emission peak around 363 nm for ZnO thin film. The energy band gap obtained for ZnO, Mg<inf>x</inf>Zn<inf>1-x</inf>O, and Cd<inf>x</inf>Zn<inf>1-x</inf>O were 3.36 eV, 3.86 eV, and 2.89 eV, respectively, as measured by Ultraviolet–Visible spectroscopy. The higher amount of photocurrent was detected in illumination condition compared to dark condition with responsivity 0.54 AW-1 for ZnO films, making it suitable for photodiodes applications. © 2020 Elsevier Ltd