51 research outputs found
Electrical observation of a tunable band gap in bilayer graphene nanoribbons at room temperature
We investigate the transport properties of double-gated bilayer graphene
nanoribbons at room temperature. The devices were fabricated using conventional
CMOS-compatible processes. By analyzing the dependence of the resistance at the
charge neutrality point as a function of the electric field applied
perpendicular to the graphene surface, we show that a band gap in the density
of states opens, reaching an effective value of ~sim50 meV. This demonstrates
the potential of bilayer graphene as FET channel material in a conventional
CMOS environment.Comment: 3 pages, 3 figure
Non-volatile switching in graphene field effect devices
The absence of a band gap in graphene restricts its straight forward
application as a channel material in field effect transistors. In this letter,
we report on a new approach to engineer a band gap in graphene field effect
devices (FED) by controlled structural modification of the graphene channel
itself. The conductance in the FEDs is switched between a conductive "on-state"
to an insulating "off-state" with more than six orders of magnitude difference
in conductance. Above a critical value of an electric field applied to the FED
gate under certain environmental conditions, a chemical modification takes
place to form insulating graphene derivatives. The effect can be reversed by
electrical fields of opposite polarity or short current pulses to recover the
initial state. These reversible switches could potentially be applied to
non-volatile memories and novel neuromorphic processing concepts.Comment: 14 pages, 4 figures, submitted to IEEE ED
High On/Off Ratios in Bilayer Graphene Field Effect Transistors Realized by Surface Dopants
The unique property of bilayer graphene to show a band gap tunable by
external electrical fields enables a variety of different device concepts with
novel functionalities for electronic, optoelectronic and sensor applications.
So far the operation of bilayer graphene based field effect transistors
requires two individual gates to vary the channel's conductance and to create a
band gap. In this paper we report on a method to increase the on/off ratio in
single gated bilayer graphene field effect transistors by adsorbate doping. The
adsorbate dopants on the upper side of the graphene establish a displacement
field perpendicular to the graphene surface breaking the inversion symmetry of
the two graphene layers. Low temperature measurements indicate, that the
increased on/off ratio is caused by the opening of a mobility gap. Beside field
effect transistors the presented approach can also be employed for other
bilayer graphene based devices like photodetectors for THz to infrared
radiation, chemical sensors and in more sophisticated structures such as
antidot- or superlattices where an artificial potential landscape has to be
created.Comment: 4 pages, 4 figure
Oxygen Surface Functionalization of Graphene Nanoribbons for Transport Gap Engineering
Erratum: Apparent rippling with honeycomb symmetry and tunable periodicity observed by scanning tunneling microscopy on suspended graphene [Phys. Rev. B 94 , 184302 (2016)]
Current Saturation and Voltage Gain in Bilayer Graphene Field Effect Transistors
The emergence of graphene with its unique electrical
properties
has triggered hopes in the electronic devices community regarding
its exploitation as a channel material in field effect transistors.
Graphene is especially promising for devices working at frequencies
in the 100 GHz range. So far, graphene field effect transistors (GFETs)
have shown cutoff frequencies up to 300 GHz, while exhibiting poor
voltage gains, another important figure of merit for analog high frequency
applications. In the present work, we show that the voltage gain of
GFETs can be improved significantly by using bilayer graphene, where
a band gap is introduced through a vertical electric displacement
field. At a displacement field of −1.7 V/nm the bilayer GFETs
exhibit an intrinsic voltage gain up to 35, a factor of 6 higher than
the voltage gain in corresponding monolayer GFETs. The transconductance,
which limits the cutoff frequency of a transistor, is not degraded
by the displacement field and is similar in both monolayer and bilayer
GFETs. Using numerical simulations based on an atomistic <i>p</i><sub><i>z</i></sub> tight-binding Hamiltonian we demonstrate
that this approach can be extended to sub-100 nm gate lengths
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