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High-speed graphene-silicon-graphene waveguide PDs with high photo-to-dark-current ratio and large linear dynamic range

Two-dimensional materials (2DMs) meet the demand of broadband and low-cost photodetection on silicon for many applications. Currently, it is still very challenging to realize excellent silicon-2DM PDs. Here we demonstrate graphene-silicon-graphene waveguide PDs operating at the wavelength-bands of 1.55 μm and 2 μm, showing the potential for large-scale integration. For the fabricated PDs, the measured responsivities are respectively ~0.15 mA/W and ~0.015 mA/W for the wavelengths of 1.55 μm and 1.96μm. In particular, the PDs exhibit a high bandwidth of ~33 GHz, an ultra-low dark current of tens of pico-amperes, a high normalized photo-to-dark-current ratio (NPDR) of 1.63x10^6 W^-1, as well as a high linear dynamic range of 3 μW-1.86 mW (and beyond) at 1.55 μm. According to the measurement results for the wavelength-bands of 1.55/2.0 μm and the theoretical modeling for the silicon-graphene heterostructure, it is revealed that internal photo-emission and photo-assisted thermionic field emission dominantly contribute to the photoresponse in the graphene-silicon Schottky junctions, which helps the future work to further improve the performance.