posted on 2020-03-12, 12:03authored byZhizhen Ma, Kazuya Kikunaga, Hao Wang, Shuai Sun, Rubab Amin, Rishi Maiti, Mohammad H. Tahersima, Hamed Dalir, Mario Miscuglio, Volker J. Sorger
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.