Speed enhancement of Ultraviolet photodetector base on ZnO quantum dots by oxygen adsorption on surface defects

Abstract Applications of ZnO quantum dots (QDs) in photodetectors are generally limited by a slower response speed and a higher dark current. The corresponding mechanism is not very clear, and how to resolve these problems is still in big challenge. Herein, we have demonstrated a photodetector on 700 nm-thick ZnO QDs film with a large number of oxygen vacancy defects by adjusting the ratio of the reactants and the reaction time. The device exhibits a quick response speed with a rise time of ~1.00 s and a recovery time of ~0.19 s. Meanwhile, the dark current and the responsivity under 730 μW/cm2 UV light illumination were found to be 20 pA and 260 mA/W under 10 V bias, respectively. The mechanism of these phenomena has been investigated, and the fast response speed of ZnO QDs photodetector in the air should originate from the adsorption/desorption of oxygen on the surface oxygen vacancy defects of ZnO QDs. The findings in this work can be used to guide design of high-performance photodetectors based on ZnO QDs and other nanomaterials with large surface to volume ratio.