Nanocavity-enhanced 3D-graphene/InP heterojunction for broad-spectral photodetection and information encryption

Indium phosphide (InP)-based photodetectors hold promise for optical communication and imaging due to excellent electron mobility. However, the intrinsic bandgap (1.34 eV) restricts photoresponse, especially in the long-wavelength near-infrared region. This study developed a super-bandgap photodetector based on a nanocavity-enhanced three-dimensional (3D) graphene/InP Schottky heterojunction via plasma-enhanced chemical vapor deposition. The high conductivity and nanocavity structure of 3D-graphene enhance light trapping and interfacial carrier modulation. Benefiting from broad-spectrum absorption by 3D-graphene and the built-in electric field within InP, the detection range extends from the intrinsic limit of 920–1550 nm, surpassing the conventional bandgap constraint. Under 1550 nm illumination, the photodetector demonstrates self-powered operation, a responsivity of 12.2 A/W, specific detectivity of 2.1 × 1010 Jones, and fast photoresponse with rise and fall times of 510 and 319 μs, respectively. The −3 dB bandwidth reaches 400 Hz. Additionally, the device exhibits excellent stability over 200 switching cycles and 3 months of storage. The photodetectors are applied to secure information encryption in the near-infrared field. This work shows that nanocavity-enhanced light trapping and interface control can extend the detection range of narrow-bandgap semiconductors, offering a versatile approach for next-gen optoelectronic devices.