Unveiling high responsivity in on-chip photodetectors with graphene Interposed between amorphous and crystalline silicon

In this study, we present an integrated graphene-based photodetector designed for operation around 1550 nm. Our design features a composite waveguide structure consisting of hydrogenated amorphous silicon, graphene, and crystalline silicon. By positioning graphene within this waveguide, we optimize the interaction between the guided mode and the traps at the graphene/amorphous silicon interface. These traps release charge carriers into graphene upon illumination, modulating the thermionic current at the graphene/crystalline silicon Schottky junction. We developed a fabrication protocol compatible with CMOS processes, preserving the integrity of the graphene layer, as confirmed by Raman spectra. The maximum measured responsivity is 1.9 A/W at 1535 nm, corresponding to an external quantum efficiency of 153 %, and a noise equivalent power of 9.6 pW/Hz−1/2. The manufacturing process is flexible and does not require sub-micron lithography. Additionally, reducing incident optical power enhances the photodetector responsivity, making it ideal for power monitoring applications in photonic integrated circuits.