Influence of ZnO buffer layers on the optoelectronic properties in Ga-doped ZnO thin films prepared by RF magnetron sputtering on PET substrates

The influence of ZnO buffer layers on the optoelectronic properties in Ga-doped ZnO (GZO) thin films deposited on polyethylene terephthalate (PET) substrates by RF magnetron sputtering was investigated. The resistivity in GZO/ZnO bilayer films decreases significantly more than one order of magnitude than that in GZO film without a ZnO buffer layer. X-ray diffraction results show that the significant improvement of electrical properties is not related to the crystalline quality. Based on X-ray photoelectron spectroscopy analysis, it is suggested that the decrease in resistivity after the introduction of ZnO buffer layers is ascribed to the restraint of diffusion of moisture and gas from PET substrates to GZO thin films. The moisture and gas diffused into GZO films will be absorbed on the films’ surface in the form of negatively charged oxygen species acting as acceptors. Fifty nm buffer layer is thick enough to achieve the best effect, with further increase of the ZnO buffer layer thickness, the resistivity in the samples will increase due to the parallel effect of ZnO and GZO layers. The introduction of ZnO buffer layers has no obvious influence on the average transmittance in the visible range which is ~90 % high for all samples.