  Graphene is a promising candidate for optoelectronic applications. In this
report, a double gated bilayer graphene FET has been made using a combination
of electrostatic and electrolytic gating in order to form an abrupt p-n
junction. The presence of two Dirac peaks in the gating curve of the fabricated
device confirms the formation of a p-n junction. At low temperatures, when the
electrolyte is frozen intentionally, the photovoltage exhibits a six-fold
pattern indicative of the hot electron induced photothermoelectric effect that
has also been seen in graphene p-n junctions made using metallic gates. We have
observed that the photovoltage increases with decreasing temperature indicating
a dominant role of supercollision scattering. Our technique can also be
extended to other 2D materials and to finer features that will lead to p-n
junctions which span a large area, like a superlattice, that can generate a
larger photoresponse. Our work creating abrupt p-n junctions is distinct from
previous works that use a source-drain bias voltage with a single ionic gate
creating a spatially graded p-n junction.
