Decoupling Dark Current and Photogain in Silicon-Based Graphene Architecture for Multidimensional Photodetection

Silicon-graphene architecture holds significant promise in the field of wafer-level process-compatible and high-performance optoelectronic device development. Despite the fact that graphene exhibits ultrabroadband absorption, silicon-based graphene photodetectors generally present low specific detectivity (D*) limited by the zero-bandgap nature and the poor light absorption. Different from traditional doping or metasurface design, this work systematically investigates the layer-dependent behavior of the photoresponse of non-equilibrium carriers in a back-gate-controlled Si/SiO2/graphene architecture. In single-layer graphene, the lack of dielectric screening causes photoconductance gain to be inevitably accompanied by a sharp increase in dark current. Conversely, the strong Thomas−Fermi screening in multilayer graphene (MLG) attenuates the global electric field penetration, achieving a synergy between dark current suppression and photocurrent gain. Under 365 nm UV excitation, the MLG device achieves D* = 1.27×1010 Jones in the steady-state negative photoconductance mode (NPC, Vbg=−22 V). In the deeply biased positive photoconductance mode (PPC, Vbg=−32 V), the external quantum efficiency (EQE) and responsivity (R) are enhanced to 52.5% and 154.6 mA/W, respectively. Furthermore, the device exhibits multidimensional photodetection capabilities at room temperature, encompassing both spectral (ultraviolet to near-infrared) and intensity (weak to strong) dimensions. Enabled by the reconfigurable switching of the photoresponse polarity, the photocurrent in each wavelength band achieves an effective photocurrent enhancement factor of approximately 2 orders of magnitude compared to the zero-gate state.