3 research outputs found
Photoresponse of an Electrically Tunable Ambipolar Graphene Infrared Thermocouple
We explore the photoresponse of an
ambipolar graphene infrared
thermocouple at photon energies close to or below monolayer grapheneās
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
Graphene/MoS<sub>2</sub> Hybrid Technology for Large-Scale Two-Dimensional Electronics
Two-dimensional (2D) materials have
generated great interest in
the past few years as a new toolbox for electronics. This family of
materials includes, among others, metallic graphene, semiconducting
transition metal dichalcogenides (such as MoS<sub>2</sub>), and insulating
boron nitride. These materials and their heterostructures offer excellent
mechanical flexibility, optical transparency, and favorable transport
properties for realizing electronic, sensing, and optical systems
on arbitrary surfaces. In this paper, we demonstrate a novel technology
for constructing large-scale electronic systems based on graphene/molybdenum
disulfide (MoS<sub>2</sub>) heterostructures grown by chemical vapor
deposition. We have fabricated high-performance devices and circuits
based on this heterostructure, where MoS<sub>2</sub> is used as the
transistor channel and graphene as contact electrodes and circuit
interconnects. We provide a systematic comparison of the graphene/MoS<sub>2</sub> heterojunction contact to more traditional MoS<sub>2</sub>-metal junctions, as well as a theoretical investigation, using density
functional theory, of the origin of the Schottky barrier height. The
tunability of the graphene work function with electrostatic doping
significantly improves the ohmic contact to MoS<sub>2</sub>. These
high-performance large-scale devices and circuits based on this 2D
heterostructure pave the way for practical flexible transparent electronics
Graphene-Based Thermopile for Thermal Imaging Applications
In
this work, we leverage grapheneās unique tunable Seebeck coefficient
for the demonstration of a graphene-based thermal imaging system.
By integrating graphene based photothermo-electric detectors with
micromachined silicon nitride membranes, we are able to achieve room
temperature responsivities on the order of ā¼7ā9 V/W
(at Ī» = 10.6 Ī¼m), with a time constant of ā¼23 ms.
The large responsivities, due to the combination of thermal isolation
and broadband infrared absorption from the underlying SiN membrane,
have enabled detection as well as stand-off imaging of an incoherent
blackbody target (300ā500 K). By comparing the fundamental
achievable performance of these graphene-based thermopiles with standard
thermocouple materials, we extrapolate that grapheneās high
carrier mobility can enable improved performances with respect to
two main figures of merit for infrared detectors: detectivity (>8
Ć 10<sup>8</sup> cm Hz<sup>1/2</sup> W<sup>ā1</sup>) and
noise equivalent temperature difference (<100 mK). Furthermore,
even average graphene carrier mobility (<1000 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup>) is still sufficient to detect
the emitted thermal radiation from a human target