Fabrication and characterization of W-doped ZnO thin films for next generation photodetector device applications

In this study, tungsten (W)-doped ZnO thin films were successfully deposited on (100)-oriented p-type silicon (p-Si) substrates via the sol-gel spin-coating method at 500 °C, with W/Zn atomic ratios varying between 0% and 4%. The sample with 2% W doping exhibited the most favorable UV photodetector characteristics, displaying diode-like rectifying behavior in the dark with a rectification ratio of 5587 at ±5 V, a responsivity of 3.84 A/W, and a photosensitivity of 34 under 365 nm UV illumination at 0.5 mW/cm². The enhanced performance at this doping level is attributed to reduced carrier recombination and improved carrier separation in the depletion region, highlighting the critical role of W doping in device optimization. In the second stage, silver nanoparticles (Ag NPs) were deposited on the optimized 2% W-doped ZnO/p-Si photodetector. Top-view and cross-sectional SEM analysis confirmed a uniform Ag NP coating with a total film thickness of 167 nm. UV-Vis spectroscopy revealed that the Ag NP-coated film had an average optical transmittance of 79.5% and an optical bandgap of 3.17 eV. The incorporation of Ag NPs significantly improved the optoelectronic performance of the device, resulting in a responsivity of 4.83 A/W, a photosensitivity of 60.82, and a detectivity of 5.06 × 10¹² Jones. Overall, the findings demonstrate that the combination of optimal W doping and metal nanoparticle integration substantially enhances the UV detection performance of ZnO/Si-based heterojunction photodetectors.