Spatial light trapping in vertical graphene/silicon heterojunctions for dual-wavelength signal recognition

Abstract

Silicon (Si)-based 1550 nm near-infrared photodetection is limited by weak long-wavelength absorption, while planar graphene suffers from limited optical absorption, hampering its use in Si-compatible photodetectors. Herein, a spatially tunable vertical graphene (VG)/Si heterostructure photodetector was fabricated by plasma-enhanced chemical vapor deposition. This study examines how the spatial design of VG arrays, including height, density, and porosity, affects light trapping, interfacial absorption, and overall device performance. Finite-difference time-domain simulations and absorption spectra showed that the optimized 750 nm VG architecture enhances light trapping and interfacial absorption, increasing 1550 nm absorption from 10% to 79%. Scanning Kelvin probe microscopy reveals a rise in carrier separation and transport. With the VG/Si heterojunction optimized at 750 nm, self-driven broadband photodetection from 440 to 1550 nm was achieved without external bias. At 1550 nm, the device exhibits a low noise power spectral density of 3.35 × 10−16 A2/Hz. Under −1 V bias, it achieves 53 A/W responsivity and a noise-limited specific detectivity of 1.3 × 1011 Jones, with a −3 dB bandwidth of 1100 Hz and rise/fall times of 142/116 μs. It maintains stable performance after 120 switching cycles and 4 months of storage. The device enables thresholded dual-wavelength optical-signal recognition at 980 and 1550 nm. This work provides a strategy for regulating optical fields and carrier dynamics in Si-compatible near-infrared photodetectors and on-chip photonic devices.