Bias‐Switchable UV‐Broadband Dual‐Mode Photodetector Enabled by a WSe 2 /GaN Vertical Heterojunction

ABSTRACT Broadband photodetectors are essential for emerging applications such as intelligent vision, optical communication, and autonomous sensing. However, conventional multispectral photodetectors often require external spectral‐selection optics or rely on architectures with fixed spectral functionality, limiting electrical reconfigurability and adaptive multifunctionality. Here, we report a bias‐tunable photodetector based on a vertical WSe 2 /GaN van der Waals heterostructure formed by integrating multilayer WSe 2 with freestanding GaN films. Benefiting from the complementary absorption of GaN and WSe 2 , the photodetector exhibits a broadband photoresponse from 300 to 900 nm. More importantly, it demonstrates a bias‐switchable dual‐mode operation: under reverse bias, the device operates as a ultraviolet (UV)‐selective photodetector, whereas under forward bias it switches to broadband detection. This behavior originates from the interplay between bias‐modulated asymmetric valence‐band offsets and spatially selective light absorption. Furthermore, the vertical configuration and type‐II band alignment significantly shorten the carrier transport path and enables ultrafast carrier extraction. As a result, the device achieves an ultra‐low dark current (∼10 −12 A) and fast rise/decay times of 34/37 µs, nearly three orders of magnitude faster than lateral heterojunction counterparts. This work elucidates the physics of bias‐dependent carrier transport in vertical WSe 2 /GaN heterojunctions and establishes a versatile platform for adaptive, multifunctional, and highly integrated optoelectronic devices.