High-responsivity graphene/silicon-heterostructure waveguide photodetectors

Graphene-based photonic devices, such as ultrafast photodetectors, optical modulators and tunable surface plasmon polariton devices, have experienced rapid development in recent years because they benefit greatly from graphene's strong field-controlled optical response. Here, we demonstrate a graphene/silicon- heterostructure photodiode formed by integrating graphene onto a silicon optical waveguide on a silicon-on-insulator (SOI) with a near to mid-infrared operational range. The waveguide enables absorption of evanescent light that propagates parallel to the graphene sheet, which results in a responsivity as high as 0.13 A W -1 at a 1.5 V bias for 2.75 μm light at room temperature. A photocurrent dependence on bias polarity was observed and attributed to two distinct mechanisms for optical absorption, that is, direct and indirect transitions in graphene at 1.55 μm and 2.75 μm, respectively. Our result demonstrates the use of in-plane absorption in a graphene-monolayer structure and the feasibility of exploiting indirect transitions in graphene/silicon- heterostructure waveguides for mid-infrared detection.