Effect of Gallium Interlayer in ZnO and Al-doped ZnO Thin Films

Abstract

Copyright © Taylor & Francis Group, LLC. For applications in the field of optoelectronics, zinc oxide (ZnO) based transparent conducting oxide thin films such as aluminium-doped zinc oxide (AZO) have recently received much attention. It is one of the most promising alternative materials to the widely used indium tin oxide (ITO or tin-doped indium oxide) and fluorine-doped tin oxide (FTO). In this work, the ZnO and AZO base thin films were prepared by radio frequency (rf) magnetron sputtering technique using ZnO and AZO (1at%Al) ceramic target. The Ga interlayer films, added in between base thin films (ZnO and AZO), were deposited by evaporation technique. Both ZnO/Ga/ZnO and AZO/Ga/AZO multilayer thin film structures were grown on glass substrates. Then the obtained multilayer structures were annealed in argon (Ar) ambient at 400°C for 1 hr. The morphology, qualitative and quantitative elemental analysis, crystal structure, electrical properties, and optical properties of the multilayer thin films were characterized by field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), a four-point probe method and UV-Vis spectroscopy. The results revealed that after annealing treatment, the average transmittance of the both multilayer thin films in visible region was improved due to a decrease in surface roughness resulting in an increase in crystalline surface. Furthermore, the results revealed lower sheet resistance in the AZO/Ga/AZO relative to pure ZnO multilayer base thin films. The significance of the electrical properties of the AZO/Ga/AZO films can be achieved due to local structure of Al site in ZnO and partial diffusion of Ga atoms into the base thin film layers. This indicates that the Ga interlayer in both ZnO/Ga/ZnO and AZO/Ga/AZO multilayer thin films can be used to further improve electrical conductivity without degrading optical transmission. © 2015