Transparent ZnO Nanostructured Thin- Film Flexible UV Photodetectors

In this study, nanostructured ZnO thin film photodetectors have been synthesized on transparent poly(ethylene terephthalate) (PET) and polyimide (PI) flexible substrates by radio frequency sputtering technology. Effect of growth temperature and oxygen flow rate on the crystallinity, optical transparency and light sensitivity of ZnO thin films were systematically investigated. XRD results reveal that ZnO thin films grown on both flexible substrates exhibit (002) cplane oriented crystallinity. The crystalline quality of ZnO films greatly depends on the surface state of the flexible substrates, substrate temperature as well as oxygen concentration during growth. The average optical transparency is above 85% in the wavelength range of 300-1000 nm for these ZnO film samples on flexible substrates. Photoluminescence properties of ZnO films on both PET and PI substrates show no obvious band-edge emission, but high intensity of emission from defects. XPS results indicate that good stoichiometry composition transfer from the target to the films has been achieved by RF magnetron sputtering. Interdigital electrode (IDE) planar photodetector devices have been fabricated on PI substrates with Ag as the top electrode. The I-V characteristics of flexible ZnO PDs reveal good light detecting response with 3.8x10(-7) A photocurrents at light power current of 40A.