Impressive Response of Spin-Coated ZnO Nanoparticle UV-Sensitive Devices with Various Thicknesses under Different UV Intensities

We fabricated ultraviolet (UV) detectors based on spin-coated pure zinc oxide (ZnO) nanoparticles with a metal–semiconductor–metal configuration. Devices with various ZnO layer thicknesses were characterized under different UV intensities, and their responsivity, sensitivity, response time, and recovery time analyzed. The following performance was achieved: responsivity of 99.8 A W⁻¹, sensitivity of 531.1, and response and recovery times of 0.01 s and 0.07 s, respectively. Increasing the thickness revealed monotonic effects on each property: the responsivity decreased, the sensitivity decreased, and the response and recovery times increased, mainly because of the thin penetration depth of ZnO and the lengthened cracks on the thicker layer. However, the effects of the UV intensity on the parameters were not monotonic. Indeed, as the intensity was increased, the responsivity decreased, the sensitivity first increased then decreased, the response time first increased before shortening, while the recovery time consistently shortened. Such trends resulted from the combination of several mechanisms: shrinkage of depletion layers, saturation of excitons, and saturation of trapping states. Increasing the radiation-on time shortened both the response and recovery times. This device performance is impressive compared with devices with more complicated material formats, device structure, or fabrication methods. Some complications in the work are also discussed.