An Inorganic/Organic Hybrid Phototransistor with Gate-Tunable Response and Broad-Spectrum Detection for Pulse Oximetry

High-performance, broad-spectrum detection spanning the visible to the near-infrared region is critical for applications such as image sensing, optical communications, and health monitoring. Although inorganic/organic hybrid phototransistors (HPTs) have been explored for such applications, a universal design strategy for material combinations and a thorough understanding of the gate-modulated photocurrent generation mechanism in these HPTs are still required. In this work, we demonstrate an inorganic/organic HPT by integrating a high-mobility, solution-processed amorphous metal oxide semiconductor with a photosensitive organic bulk heterojunction. Thanks to the rational type-II band alignment, this heterostructure efficiently decouples carrier generation and transport processes, thus introducing a photogating effect. By strategically gate-modulating the dominant photocurrent generation mechanism from photoconductive to photogating effects, the device achieves a maximum sensitivity of ∼10⁴, specific detectivity of 1.5 × 10¹² Jones, and responsivity of 1.0 × 10⁴ A W^-1 under 808 nm illumination. Furthermore, the HPT also exhibits a broadband photodetection capability as well as excellent operational stability in an ambient environment. These attributes make our HPT a sensitive detection unit for pulse oximetry sensing without requiring any external amplification circuits. The results of this study highlight the potential of this hybrid design approach for tailoring optoelectronic properties, thus offering a promising pathway for practical applications demanding weak signal detection across broad spectral ranges.