Photoresponse of an Electrically Tunable Ambipolar
Graphene Infrared Thermocouple
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Abstract
We explore the photoresponse of an
ambipolar graphene infrared
thermocouple at photon energies close to or below monolayer graphene’s
optical phonon energy and electrostatically accessible Fermi energy
levels. The ambipolar graphene infrared thermocouple consists of monolayer
graphene supported by an infrared absorbing material, controlled by
two independent electrostatic gates embedded below the absorber. Using
a scanning infrared laser microscope, we characterize these devices
as a function of carrier type and carrier density difference controlled
at the junction between the two electrostatic gates. On the basis
of these measurements, conducted at both mid- and near-infrared wavelengths,
the primary detection mechanism can be modeled as a thermoelectric
response. By studying the effect of different infrared absorbers,
we determine that the optical absorption and thermal conduction of
the substrate play the dominant role in the measured photoresponse
of our devices. These experiments indicate a path toward hybrid graphene
thermal detectors for sensing applications such as thermography and
chemical spectroscopy