Metal-Free All Transparent Zinc Oxide-Based Ultraviolet Photodetectors With Simple Bilayer Structure

Ultraviolet (UV) radiation harms humans and has a chronic effect on the skin and eyes. This article presents a metal-free, highly transparent zinc oxide-based UV sensor. To avoid the interface mismatch, gallium-doped zinc oxide (GZO) is used as the top electrode, which has very low resistivity to play the role of the transparent interdigital electrode on top of the device to maintain the transmittance. The GZO/ZnO photoconductor configuration is prepared by sputtering the films at room temperature on the glass substrate. For the material and device properties, X-ray diffraction (XRD), UV-visible spectroscopy, scanning electron microscope (SEM), and semiconductor parameter analyzer are used. The high visible transmittance is over 85%, with excellent sensitivity under the UV light density of 4 mW/cm2 with a wavelength of 365 nm. The device performance is not only based on the photoconductive effect but also the pyro-photonic effect of reducing the persistent photoconductivity (PPC), which enhances the response time. Without a mismatch between the interface, the externally applied bias does not affect the dark current. This simple structure provides nice transmittance over 85% with a small external applied bias 1 V that causes a 3-order ON-OFF ratio. This work offers a highly transparent ZnO-based photoconductor with an excellent response speed. To the best of our knowledge, it is the first report about all ZnO-based UV photodetectors (zinc composition as metal is over 95%).