Compact Graphene Plasmonic Slot Photodetector on Silicon-on-Insulator with High Responsivity

Graphene has extraordinary electro-optic properties and is therefore a promising candidate for monolithic photonic devices such as photodetectors. However, the integration of this atom-thin layer material with bulky photonic components usually results in a weak light–graphene interaction, leading to large device lengths, limiting electro-optic performance. In contrast, here we demonstrate a plasmonic slot graphene photodetector on silicon-on-insulator platform with high responsivity of 0.7 A/W given a just 5 μm short device length. We observe that the maximum photocurrent and, hence, the highest responsivity, scales inversely with the slot width. Using a dual-lithography step, we realize 15 nm narrow slots that show a 30× higher responsivity per unit device-length when compared to photonic graphene photodetectors. Furthermore, we reveal that the back-gated electrostatics is overshadowed by channel-doping contributions induced by the contacts of this ultrashort channel graphene photodetector. This leads to quasi charge neutrality, which explains both the previously unseen offset between the maximum photovoltaic-based photocurrent relative to graphene’s Dirac point and the observed nonambipolar transport characteristics. Such micrometer-compact and absorption-efficient photodetectors allow for short-carrier pathways in next-generation photonic components, while being offering a testbed for studying short-channel carrier physics in graphene optoelectronic devices.