Self‐Powered Visible‐Blind Graphene/NiO/ZnO UV‐C Photodiodes

ABSTRACT Continuous monitoring of deep‐ultraviolet (UV‐C) radiation is crucial for applications ranging from germicidal sterilization to secure communications. While metal‐oxide semiconductors offer a scalable alternative to costly SiC or AlGaN technologies, their performance is typically bottlenecked by the lack of robust ‐p‐type layers and UV‐C transparent electrodes. In this work, we demonstrate a high‐performance, self‐powered UV‐C photodiode that overcomes these limitations through a fully scalable architecture. We address the transparency constraint by utilizing graphene, directly synthesized via low‐temperature plasma‐enhanced chemical vapor deposition on sapphire, as a highly transparent hole‐collecting anode. A vertical p‐NiO/n‐ZnO heterojunction is subsequently fabricated via magnetron sputtering, capped with a UV‐C reflective aluminum mirror. By tuning the oxygen stoichiometry during sputtering, we induce nickel vacancy acceptors that significantly enhance the p‐NiO conductivity and junction quality. Operating in self‐powered mode, the device delivers a peak responsivity of 7.9 mA/W under 261 nm excitation and a UV‐to‐visible rejection ratio of > 10 2 . It also exhibits rapid response times <50 ms and an exceptional ON/OFF ratio of 10 4 . These findings establish graphene integrated with optimized metal oxides as a viable route toward low‐cost, large‐area UV‐C optoelectronics.