Vertical Graphene/Violet-Phosphorus/Graphene Photodetectors for Wavelength-Programmed Optical Signal Encoding

As an emerging two-dimensional van der Waals material, violet phosphorus is particularly notable for its ambient stability, moderate bandgap, and strong light absorption, making it an excellent candidate for photodetection applications. However, conventional lateral-channel devices based on violet phosphorus typically suffer from severe carrier recombination losses over extended transport distances. Here, we demonstrate a high-performance vertical-channel photodetector based on a graphene/violet phosphorus/graphene (Gr/VP/Gr) van der Waals heterostructure. By shortening the carrier transport path, the vertical architecture enables efficient carrier collection and a high photoconductive gain. Under 532 nm illumination, the device achieves a responsivity of 1.7 × 104 A/W, a specific detectivity of 2.1 × 1013 Jones, and an external quantum efficiency of approximately 3.9 × 106%; its photoresponse spans 450-1050 nm. A transport-scaling analysis comparing vertical and lateral geometries indicates that the vertical structure reduces the carrier drift transit time to the picosecond scale, providing a quantitative rationale for the large effective gain. The device also exhibits wavelength-dependent transient dynamics, with a relatively fast response at 450 nm and a persistent response at 800 nm. These distinct temporal signatures enable a proof-of-concept demonstration of wavelength-programmed optical signal encoding. The outstanding optoelectronic performance of Gr/VP/Gr vertical heterostructures establishes them as an innovative and versatile platform for next-generation broadband photodetection and secure optical data transmission systems with enhanced quantum efficiency and spectral adaptability.