Broadband Quantum‐Junction Photodiode Achieving Ultralow‐Noise Light Sensing

Abstract Low‐noise photodetectors hold immense promise for advancing weak‐light sensing in cutting‐edge applications such as health monitoring, intelligent driving, and military surveillance. Quantum‐junction photodiode (QJPD), composed solely of light‐absorbing quantum dots, are highly expected to overcome the noise limitation of conventional narrow‐bandgap semiconductor photodetectors due to their inherent advantages of low hot carrier density as well as weak inter‐dot electronic coupling. However, the targeted device engineering of QJPD remains a critical exploration area to fully unlock their low‐noise potential. Here, a low‐noise, broadband QJPD is proposed through the strategic incorporation of an ultrathin ALD SnO x layer. This SnO x modification efficiently suppresses the interfacial barrier, reduces the interface resistance and minimizes dark current of QJPDs. Consequently, SnO x ‐modified QJPDs achieve an ultralow noise current of 4.85 × 10 −14 A Hz⁻ 1/2 and a specific detectivity exceeding 10 12 Jones across a broad spectral range (350−1050 nm), significantly outperforming unmodified QJPDs (≈10 10 Jones) and other n‐i‐p quantum dot photodetectors (≈10 9 Jones). SnO x ‐modified QJPDs enable high‐accuracy blood oxygen saturation measurements using near‐infrared light and real‐time heartbeat monitoring under weak ambient light conditions. This work establishes a foundation for the development of low‐noise QJPDs, underscoring their potential for weak‐light detection in challenging environments with strong hindering and ambient light.