Broadband light-trapping enhancement of graphene absorptivity

Low optical absorptivity of graphene limits the quantum efficiency of graphene-based optoelectronic devices. We demonstrate a broadband enhancement of absorptivity in an architecture of graphene intercalation inside a simple-cubic woodpile photonic crystal. Significant light-trapping effect is achieved due to spectrally broad and dense resonances in the architecture, especially modes propagating nearly parallel to the interface between the photonic crystal and the background material. We demonstrate an overall absorptivity $\ensuremath{\sim}10$ to 17 times larger than the free-standing bare graphene monolayer with bandwidth to central frequency ratio 0.3, and $\ensuremath{\sim}5$ to 11 times larger with bandwidth to central frequency ratio 1.33. A distributed intercalation of three graphene monolayers proves a $\ensuremath{\sim}70%$ overall absorptivity with bandwidth to central frequency ratio 0.3.