been shown to operate as high-speed photodetectors [3] with response times comparable to conventional silicon-based devices, but the absence of a bandgap and lack of significant gain mechanism limits their use for ultrasensitive light detection. Hybrid structures of graphene with semiconductor materials such as quantum dots, [4][5][6] chlorophyll molecules, [7] and MoS 2 [8][9][10] have been shown to enhance light absorption and provide an internal gain mechanism. However, these implementations typically have a limited operational bandwidth of less than 10 Hz which hampers their use in real world applications.Slow response times in these systems are produced by the long-lived trapping of charges, often manifested as hysteresis in gate-voltage sweeps. This has been observed in organic, carbon nanotubes, graphene, and more recently in transitionmetal dichalcogenide (TMD) field-effect transistors and is typically attributed to unavoidable intrinsic and/or extrinsic charge traps, e.g., SiO 2 surface states [11][12][13][14] and atmospheric contamination. [12,13,[15][16][17] To reduce the impact of such traps, various solutions have been explored including gate-voltage pulses, [11,18,19] vacuum annealing, [20,21] and ionic-liquid gating. [22,23] Although ionic-liquid gating has been utilized in WS 2 phototransistors [24] and MoTe 2 -graphene photodetectors, [25] the beneficial effect of poly mer gating on the performance of photodetectors consisting of atomically thin heterostructures has not yet been explored.In this work, we report the first study of WS 2 -graphene heterostructure photodetectors with an ionic-polymer gate. We demonstrate a gate-tunable responsivity up to 10 6 A W −1 , which is comparable with other heterostructure devices, [4][5][6][7]9,10] and surpasses that of graphene or TMD photodetectors by at least four orders of magnitude. Our devices reach a −3 dB bandwidth of 1.5 kHz, without the need for gatevoltage pulses, leading to sub-millisecond rise and fall times. The observed 10 3 -fold increase of photodetection bandwidth, when compared to other heterostructure photodetectors, is enabled by the enhanced screening properties of the mobile ions in our ionic polymer top gate, which act to compensate the charge traps limiting the speed of previous devices. Our devices have a detectivity of D* = 3.8 × 10 11 Jones, which is approaching that of single-photon counters, and are able to operate on a broad spectral range (400-700 nm). These properties make ionic-polymer-gated WS 2 -graphene photodetectors highly suitable for video-frame-rate imaging applicationsThe combination of graphene with semiconductor materials in heterostructure photodetectors enables amplified detection of femtowatt light signals using micrometer-scale electronic devices. Presently, long-lived charge traps limit the speed of such detectors, and impractical strategies, e.g., the use of large gatevoltage pulses, have been employed to achieve bandwidths suitable for applications such as video-frame-rate imaging. Here, atomically thin gr...

We fabricate planar graphene field-effect transistors with self-aligned side-gate at 100 nm from the 500 nm wide graphene conductive channel, using a single lithographic step. We demonstrate side-gating below 1 V with conductance modulation of 35% and transconductance up to 0.5 mS/mm at 10 mV drain bias. We measure the planar leakage along the SiO2/vacuum gate dielectric over a wide voltage range, reporting rapidly growing current above 15 V. We unveil the microscopic mechanisms driving the leakage, as Frenkel-Poole transport through SiO2 up to the activation of Fowler-Nordheim tunneling in vacuum, which becomes dominant at higher voltages. We report a field-emission current density as high as 1 μA/μm between graphene flakes. These findings are important for the miniaturization of atomically thin devices

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