Ultra-sensitive and plasmon-tunable graphene photodetectors for micro-spectrometry

We demonstrate an ultra-sensitive photodetector based on a graphene/monolayer MoS2 vertical heterostructure working at room temperature. Highly confined plasmon waves are efficiently excited through a periodic array of monolayer graphene ribbons in which plasmon resonance has remarkably large oscillator strength, resulting in a sharp optical absorption peak in the normal-incidence transmission spectrum. A significant amount of electron-hole pairs are produced in graphene ribbons by optical absorption, separated by the built-in electric field across the graphene/MoS2 heterojunction. The responsivity reaches up to 1 × 107 A W-1 at room temperature due to very strong resonance in the heterostructure, yielding a highly sensitive graphene-based photodetector. Additionally, the absorption can be tuned over a wide spectral range (6-16 μm) by varying gate biasing. The ultra-sensitive, spectrally tunable photodetector could be potentially used as a promising candidate for mid-infrared micro-spectrometers.