86 research outputs found
Coulomb Drag and Magnetotransport in Graphene Double Layers
We review the fabrication and key transport properties of graphene double
layers, consisting of two graphene monolayers placed in close proximity,
independently contacted, and separated by an ultra-thin dielectric. We outline
a simple band structure model relating the layer densities to the applied gate
and inter-layer biases, and show that calculations and experimental results are
in excellent agreement both at zero and in high magnetic fields. Coulomb drag
measurements, which probe the electron-electron scattering between the two
layers reveal two distinct regime: (i) diffusive drag at elevated temperatures,
and (ii) mesoscopic fluctuation-dominated drag at low temperatures. We discuss
the Coulomb drag results within the framework of existing theories.Comment: 9 pages, 6 figure
Spin-Polarized to Valley-Polarized Transition in Graphene Bilayers at in High Magnetic Fields
We investigate the transverse electric field () dependence of the =0
quantum Hall state (QHS) in dual-gated graphene bilayers in high magnetic
fields. The longitudinal resistivity () measured at =0 shows an
insulating behavior which is strongest in the vicinity of =0, and at large
-fields. At a fixed perpendicular magnetic field (), the =0 QHS
undergoes a transition as a function of , marked by a minimum,
temperature-independent . This observation is explained by a
transition from a spin polarized =0 QHS at small -fields, to a valley
(layer) polarized =0 QHS at large -fields. The -field value at which
the transition occurs has a linear dependence on Comment: 5 pages, 5 figure
Dielectric Thickness Dependence of Carrier Mobility in Graphene with HfO2 Top Dielectric
We investigate the carrier mobility in mono- and bi-layer graphene with a top
HfO2 dielectric, as a function of the HfO2 film thickness and temperature. The
results show that the carrier mobility decreases during the deposition of the
first 2-4 nm of top dielectric and remains constant for thicker layers. The
carrier mobility shows a relatively weak dependence on temperature indicating
that phonon scattering does not play a dominant role in controlling the carrier
mobility. The data strongly suggest that fixed charged impurities located in
close proximity to the graphene are responsible for the mobility degradation.Comment: 3 pages, 4 figure
Scaling Properties of Ge-SixGe1-x Core-Shell Nanowire Field Effect Transistors
We demonstrate the fabrication of high-performance Ge-SixGe1-x core-shell
nanowire field-effect transistors with highly doped source and drain, and
systematically investigate their scaling properties. Highly doped source and
drain regions are realized by low energy boron implantation, which enables
efficient carrier injection with a contact resistance much lower than the
nanowire resistance. We extract key device parameters, such as intrinsic
channel resistance, carrier mobility, effective channel length, and external
contact resistance, as well as benchmark the device switching speed and ON/OFF
current ratio.Comment: 5 pages, 4 figures. IEEE Transactions on Electron Devices (in press
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Establishing a uniformly thin dielectric layer on graphene in a semiconductor device without affecting the properties of graphene
A method and semiconductor device for forming a uniformly thin dielectric layer on graphene. A metal or semiconductor layer is deposited on graphene which is located on the surface of a dielectric layer or on the surface of a substrate. The metal or semiconductor layer may act as a nucleation layer for graphene. The metal or semiconductor layer may be subjected to an oxidation process. A thin dielectric layer may then be formed on the graphene layer after the metal or semiconductor layer is oxidized. As a result of synthesizing a metal-oxide layer on graphene, which acts as a nucleation layer for the gate dielectric and buffer to graphene, a uniformly thin dielectric layer may be established on graphene without affecting the underlying characteristics of graphene.Board of Regents, University of Texas Syste
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