The Fabrication And Characterization Of Micro-nano ZnO-based Ultraviolet Photodetectors

ZnO is one of the most important II–VI group semiconductors, which has been suggested as a promising material for various technological applications, especially for optoelectronic shortwave-length devices due to its wide and direct band gap. In addition, ZnO has many advantages such as rich morphology, variable synthetic strategies, cheap and readily available raw materials, good thermal stability, high carrier mobility, especially the very excellent radiation hardness which becomes it very suitable for using in harsh environments. In particular, the micro-nano ZnO materials have more excellent performance than bulk ZnO materials due to the small size effect and quantum size effect of micro-nano structures. Therefore, this article is intended to apply the ZnO micro-nanostructures to ultraviolet detector and rely on the advantages of nano-science itself to improve the performance of the ultraviolet detector. The main work is as follows:1. We prepared ZnO microrod with a hexagonal cross section and good crystalline property through a vapor phase transport route. Then two Ag electrodes were deposited by radio frequency magnetic sputtering, so we can construct the metal-semiconductor-metal（MSM） structure ultraviolet detector and analyze the photoresponse characteristics and mechanism of the device. Experimental results show that the dark current is only 5.0×10^-9A at 5 V bias while the photocurrent is dramatically increased to about 7.2×10^-8 A under 325 nm UV light illumination. The fitting result indicates a value of 2.02 s for the rise time and a value of 4.66 s for the decay time.2. On the basis of a single ZnO microrod ultraviolet detector, we also introduced ZnO quantum dots and the quantum dots were decorated on an individual ZnO microrod surface to construct a photodetector. As the ZnO QDs were decorated on the microrod, the device showed a more excellent UV detection performance. The photocurrent and light-to-dark current ratio were increased by about 2 magnitude orders while the response and recovery speed were accelerated by more than 1 orderof magnitude. Besides increased responsivity, the QD-decorated ZnO microrod also displayed a broader response in shorter wavelength region.3. In this paper, the graphene oxide film was obtained by self-assembly technology of graphene oxide solution. Then the graphene oxide thin film was transferred across the electrode gap of Au interdigital electrodes and reduced by ascorbic acid. We analyzed the surface structure and conductive property of graphene oxide film before and after the reduction by Raman and electrical tests. After the reduction, ZnO QDs in ethanol solution were dropped onto the reduced graphene oxide thin film. Subsequently, the MSM structure UV photodetector based on colloidal ZnO QD and reduced graphene oxide film composites was fabricated. Under325 nm UV light illumination, the device showed significant differences between light and dark current and had good repeatability and stability.