Photodeposited Amorphous WO₃ Thin-FilmConductive Filters for Heterojunction Near-Ultraviolet SpectrallySelective Photodetection and Imaging

Spectrally selective photodetectors (SSPDs) are crucial components in diverse fields, such as telecommunications, environmental surveillance, and medical diagnostics. Typically, these devices rely on external optical filters to selectively detect light within a narrow spectral band. While this scheme is effective, it adds complexity to the system architecture and raises manufacturing costs, which can also potentially lead to a decrease in sensitivity. Alternatively, the formation of heterojunctions between conductive filters and semiconductors can develop SSPDs that not only possess simplified architecture but also exhibit inherent self-filtering capabilities. In this work, we introduce an amorphous WO₃/GaN heterojunction ultraviolet SSPD that exhibits a distinct detection peak at 370 nm, with a full width at half-maximum of less than 20 nm. The WO₃ thin films were deposited photochemically under ultraviolet light by using a metal chloride precursor. The SSPD offers excellent photodetection performance, with a high photo-to-dark current ratio of 6.19 × 10⁴, a high responsivity of 495 mA/W, and an excellent specific detectivity of up to 3.31 × 10¹¹ Jones at −5 V, all of which are significantly improved compared to the crystalline WO₃/GaN device. Additionally, our SSPD shows promise for selective imaging applications within the near-UV spectrum.