Ultraviolet‐Induced Band Engineering in Black Phosphorus/Gallium Nitride Heterojunction Toward High‐Performance Broadband Photodetection

ABSTRACT Broadband photodetectors that combine ultraviolet sensitivity with visible and near‐infrared response are important for multispectral optoelectronic sensing. However, the performance of these photodetectors is often limited by weak interfacial carrier separation and inefficient gain formation. Here, we demonstrate a mixed‐dimensional van der Waals heterojunction photodetector integrating two‐dimensional black phosphorus (bP) with three‐dimensional n‐type gallium nitride (n‐GaN), enabling broadband photodetection from 255 to 1800 nm. We reveal an ultraviolet‐induced interfacial band engineering, in which two cooperative photogain pathways regulate both carrier lifetime and carrier transit time. Under ultraviolet illumination, hole trapping within GaN and charge accumulation at the bP/GaN interface simultaneously prolong the electron lifetime and shorten the tunneling transit time, producing a high photoconductive gain. By contrast, visible and near‐infrared photons are mainly absorbed by narrow‐bandgap bP, enabling broadband response through direct photocarrier generation. This wavelength‐dependent carriergeneration and transport mechanism enables a responsivity of 145.67 A W −1 and a detectivity of 1.32 × 10 12 Jones under 365 nm illumination while enabling multispectral detection across the ultraviolet‐to‐infrared range. These results establish a wavelength‐dependent band engineering strategy in mixed‐dimensional van der Waals heterojunctions and provide a promising platform for high‐performance broadband photodetection and multispectral perception.