Enhanced photoresponse of nanostructured ZnO-based flexible photodetectors

Abstract

Recently, the photoconducting response at different degrees of straining of ZnO–based nanostructured materials and devices has raised a lot of research interests. For a strained piezoelectric semiconductor, such as ZnO, an ionic displacement takes place inside ZnO inducing piezoelectric polarization that modulate the carrier concentration, transport behavior and barrier height at the interface. In this study, we report high performance ZnO-based photodetectors with enhanced photo-responsivity fabricated on flexible polyethylene terephthalate (PET) and polyimide (PI) substrates by sputtering at low temperatures. X-ray photoelectron spectroscopy results indicate that good stoichiometry composition transfer from the target to the films by using RF magnetron sputtering. The effect of growth temperature and sputtering power on the crystallinity, optical transparency and surface morphology of nanostructured ZnO thin films has been systematically investigated in this work. XRD results show that ZnO thin films grown on PI flexible substrates exhibit good (002) c-plane oriented crystallinity. Interdigital electrode (IDE) planar photodetector devices have been fabricated on PI substrates with Ag as the top electrodes. The average optical transparency is over 85% in the wavelength range of 400-800 nm for these ZnO photodetector devices on flexible PI substrates. The photocurrents of the ZnO flexible PDs on PI substrates realize an increase by three magnitudes from 10^-9 under dark conditions to 10^-6 A under a 35 mW laser excitation source.