Au-modified ZnO thin films for higher-performance ultraviolet photodetectors

ZnO-based ultraviolet (UV) photodetectors are widely studied due to their wide bandgap and higher photosensitivity. However, the ZnO thin-film UV photodetectors face higher dark current and limited gain despite their wide bandgap advantage. Here, Au overlayers (5-40 nm) were deposited on optimized 221 nm ZnO (prepared via sol-gel method) films using cost-effective spin-coating (ZnO film) and RF sputtering (Au overlayers). Au induces Schottky barriers (ϕ _Au = 5.47 eV > ϕ _ZnO = 4.45 eV) that suppress dark current down to 7.29 nA. Meanwhile, plasmonic Au nanoparticles generate localized surface plasmon resonance (LSPR) hot electrons that enhance UV absorption and photocurrent. The device with a 10 nm Au overlayer achieves an excellent photoresponse of 7.79 × 10³ and a photocurrent of 50 µA under ultra-low 24 µW cm^-2 UV illumination (365 nm). This performance surpasses literature values at lower UV intensity, also among the highest reported for ZnO detectors prepared using the sol-gel method. The optimized Au-ZnO devices also exhibit fast response (T _r = 15 s) and scalable fabrication routes. These results reveal the promise of Au/ZnO hybrid thin films for sensitive, lower-intensity UV detection with applications in flame sensing, wearable optoelectronics, and environmental monitoring.