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, MgxZn1-xO, and CdxZn1-xO thin films on silicon substrate using an electron beam evaporation system. The crystal phase purity, surface morphology, optical and electrical properties of deposited ZnO, MgxZn1-xO, and CdxZn1-xO 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 MgxZn1-xO 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, MgxZn1-xO, and CdxZn1-xO 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.