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

TL;DR

This paper demonstrates a highly compact, high-responsivity graphene plasmonic slot photodetector on silicon-on-insulator, achieving significant performance improvements through ultra-narrow slot design and revealing new electrostatic effects.

Contribution

It introduces a novel ultra-short graphene photodetector with high responsivity, utilizing plasmonic slot engineering and dual-lithography for sub-15 nm gaps, and uncovers electrostatic effects overshadowing back-gate control.

Findings

15-times higher responsivity per unit length with 15 nm slots

Responsivity scales inversely with slot gap width

Back-gate electrostatics are dominated by contact-induced doping

Abstract

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 given the 5 um-short device length. We observe that the maximum photocurrent, and hence the highest responsivity, scales inversely with the slot gap width. Using a dual-lithography step, we realize 15 nm narrow slots that show a 15-times higher responsivity per unit device-length 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 ultra-short channel graphene photodetector. This leads to quasi charge neutrality, which explains both the previously-unseen offset between the maximum photovoltaic-based photocurrent relative to graphenes Dirac point and the observed non-ambipolar transport. Such micrometer compact and absorption-efficient photodetectors allow for short-carrier pathways in next-generation photonic components, while being an ideal testbed to study short-channel carrier physics in graphene optoelectronics.