7,523 research outputs found
Electronic measurement and control of spin transport in Silicon
The electron spin lifetime and diffusion length are transport parameters that
define the scale of coherence in spintronic devices and circuits. Since these
parameters are many orders of magnitude larger in semiconductors than in
metals, semiconductors could be the most suitable for spintronics. Thus far,
spin transport has only been measured in direct-bandgap semiconductors or in
combination with magnetic semiconductors, excluding a wide range of
non-magnetic semiconductors with indirect bandgaps. Most notable in this group
is silicon (Si), which (in addition to its market entrenchment in electronics)
has long been predicted a superior semiconductor for spintronics with enhanced
lifetime and diffusion length due to low spin-orbit scattering and lattice
inversion symmetry. Despite its exciting promise, a demonstration of coherent
spin transport in Si has remained elusive, because most experiments focused on
magnetoresistive devices; these methods fail because of universal impedance
mismatch obstacles, and are obscured by Lorentz magnetoresistance and Hall
effects. Here we demonstrate conduction band spin transport across 10 microns
undoped Si, by using spin-dependent ballistic hot-electron filtering through
ferromagnetic thin films for both spin-injection and detection. Not based on
magnetoresistance, the hot electron spin-injection and detection avoids
impedance mismatch issues and prevents interference from parasitic effects. The
clean collector current thus shows independent magnetic and electrical control
of spin precession and confirms spin coherent drift in the conduction band of
silicon.Comment: Single PDF file with 4 Figure
Optical Phonon Limited High Field Transport in Layered Materials
An optical phonon limited velocity model has been employed to investigate
high-field transport in a selection of layered 2D materials for both, low-power
logic switches with scaled supply voltages, and high-power, high-frequency
transistors. Drain currents, effective electron velocities and intrinsic
cut-off frequencies as a function of carrier density have been predicted thus
providing a benchmark for the optical phonon limited high-field performance
limits of these materials. The optical phonon limited carrier velocities of a
selection of transition metal dichalcogenides and black phosphorus are found to
be modest as compared to their n-channel silicon counterparts, questioning the
utility of these devices in the source-injection dominated regime. h-BN, at the
other end of the spectrum, is shown to be a very promising material for
high-frequency high-power devices, subject to experimental realization of high
carrier densities, primarily due to its large optical phonon energy.
Experimentally extracted saturation velocities from few-layer MoS2 devices show
reasonable qualitative and quantitative agreement with predicted values.
Temperature dependence of measured vsat is discussed and found to fit a
velocity saturation model with a single material dependent fit parameter.Comment: 8 pages, 6 figure
Silicon-CMOS Compatible In-Situ CCVD Grown Graphene Transistors with Ultra-High On/Off-Current Ratio
By means of catalytic chemical vapor deposition (CCVD) in-situ grown
monolayer graphene field-effect transistors (MoLGFETs) and bilayer graphene
transistors (BiLGFETs) are realized directly on oxidized silicon substrate
without the need to transfer graphene layers. In-situ grown MoLGFETs exhibit
the expected Dirac point together with the typical low on/off-current ratios.
In contrast, BiLGFETs possess unipolar p-type device characteristics with an
extremely high on/off-current ratio up to 1E7. The complete fabrication process
is silicon CMOS compatible. This will allow a simple and low-cost integration
of graphene devices for nanoelectronic applications in a hybrid silicon CMOS
environment.Comment: 16 pages, 4 figure
Electron Mobility and Magneto Transport Study of Ultra-Thin Channel Double-Gate Si MOSFETs
We report on detailed room temperature and low temperature transport
properties of double-gate Si MOSFETs with the Si well thickness in the range
7-17 nm. The devices were fabricated on silicon-on-insulator wafers utilizing
wafer bonding, which enabled us to use heavily doped metallic back gate. We
observe mobility enhancement effects at symmetric gate bias at room
temperature, which is the finger print of the volume inversion/accumulation
effect. An asymmetry in the mobility is detected at 300 K and at 1.6 K between
the top and back interfaces of the Si well, which is interpreted to arise from
different surface roughnesses of the interfaces. Low temperature peak
mobilities of the reported devices scale monotonically with Si well thickness
and the maximum low temperature mobility was 1.9 m2/Vs, which was measured from
a 16.5 nm thick device. In the magneto transport data we observe single and two
sub-band Landau level filling factor behavior depending on the well thickness
and gate biasing
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