Tunable graphene-silicon heterojunctions for ultrasensitive photodetection.

We present the photodetection properties of graphene/Si heterojunctions both in the photocurrent and photovoltage modes. Monolayer graphene/Si junctions were found to be excellent weak-signal detectors with photovoltage responsivity exceeding 10(7) V/W and with noise-equivalent-power reaching ∼1 pW/Hz(1/2), potentially capable of distinguishing materials with transmittance, T = 0.9995 in a 0.5 s integration time. In the photocurrent mode, the response was found to remain linear over at least six decades of incident power (P), with tunable responsivity up to 435 mA/W (corresponding to incident photon conversion efficiency (IPCE) > 65%) obtained by layer thickening and doping. With millisecond-scale responses and ON/OFF ratios exceeding 10(4), these photodiodes are highly suitable for tunable and scalable broadband (400 < λ < 900 nm) photodetectors, photometers, and millisecond-response switching, spectroscopic and imaging devices, and further, and are architecturally compatible with on-chip low-power optoelectronics.