1,707 research outputs found
Weak measurement and the traversal time problem
The theory of weak measurement, proposed by Aharonov and coworkers, has been
applied by Steinberg to the long-discussed traversal time problem. The
uncertainty and ambiguity that characterize this concept from the perspective
of von Neumann measurement theory apparently vanish, and joint probabilities
and conditional averages become meaningful concepts. We express the Larmor
clock and some other well-known methods in the weak measurement formalism. We
also propose a method to determine higher moments of the traversal time
distribution in terms of the outcome of a gedanken experiment, by introducing
an appropriate operator. Since the weak measurement approach can sometimes lead
to unphysical results, for example average negative reflection times and higher
moments, the interpretation of the results obtained remains an open problem.Comment: Talk given at the Adriatico Research Conference on ``Tunnelling and
its implications'', 30 July--2 August 1996, ICTP, Triest
NANOTCAD2D: Two-dimensional code for the simulation of nanoelectronic devices and structures
In this paper we present NANOTCAD2D, a code for the simulation of the
electrical properties of semiconductor-based nanoelectronic devices and
structures in two-dimensional domains. Such code is based on the solution of
the Poisson/Schr\"odinger equation with density functional theory and of the
continuity equation of the ballistic current. NANOTCAD2D can be applied to
structures fabricated on III-IV, strained-silicon and silicon-germanium
heterostructures, CMOS structures, and can easily be extended to new materials.
In particular, in the case of SiGe heterostructures, it computes the effects of
strain on the energy band profiles. The effects of interface states at the
air/semiconductor interfaces, particularly significant in the case of devices
obtained by selective etching, are also properly taken into account.Comment: 23 pages, 11 figure
On the possibility of tunable-gap bilayer graphene FET
We explore the device potential of tunable-gap bilayer graphene FET
exploiting the possibility of opening a bandgap in bilayer graphene by applying
a vertical electric field via independent gate operation. We evaluate device
behavior using atomistic simulations based on the self-consistent solution of
the Poisson and Schroedinger equations within the NEGF formalism. We show that
the concept works, but bandgap opening is not strong enough to suppress
band-to-band tunneling in order to obtain a sufficiently large Ion/Ioff ratio
for CMOS device operation.Comment: 10 pages, 3 figures, submitted to IEEE ED
Simulation of Graphene Nanoribbon Field Effect Transistors
We present an atomistic three-dimensional simulation of graphene nanoribbon
field effect transistors (GNR-FETs), based on the self-consistent solution of
the 3D Poisson and Schroedinger equation with open boundary conditions within
the non-equilibrium Green's Function formalism and a tight-binding hamiltonian.
With respect to carbon nanotube FETs, GNR-FETs exhibit comparable performance,
reduced sensitivity on the variability of channel chirality, and similar
leakage problems due to band-to-band tunneling. Acceptable transistor
performance requires effective nanoribbon width of 1-2 nm, that could be
obtained with periodic etching patterns or stress patterns
A Three-dimensional simulation study of the performance of Carbon Nanotube Field Effect Transistors with doped reservoirs and realistic geometry
In this work, we simulate the expected device performance and the scaling
perspectives of Carbon nanotube Field Effect Transistors (CNT-FETs), with doped
source and drain extensions. The simulations are based on the self-consistent
solution of the 3D Poisson-Schroedinger equation with open boundary conditions,
within the Non-Equilibrium Green's Function formalism, where arbitrary gate
geometry and device architecture can be considered. The investigation of short
channel effects for different gate configurations and geometry parameters shows
that double gate devices offer quasi ideal subthreshold slope and DIBL without
extremely thin gate dielectrics. Exploration of devices with parallel CNTs show
that On currents per unit width can be significantly larger than the silicon
counterpart, while high-frequency performance is very promising.Comment: Submitted to IEEE TE
Shot noise in resonant tunneling structures
We propose a quantum mechanical approach to noise in resonant tunneling
structures, that can be applied in the whole range of transport regimes, from
completely coherent to completely incoherent. In both limiting cases, well
known results which have appeared in the literature are recovered. Shot noise
reduction due to both Pauli exclusion and Coulomb repulsion, and their combined
effect, are studied as a function of the rate of incoherent processes in the
well (which are taken into account by means of a phenomenological relaxation
time), and of temperature. Our approach allows the study of noise in a variety
of operating conditions (i.e., equilibrium, sub-peak voltages, second resonance
voltages), and as a function of temperature, explaining experimental results
and predicting interesting new results.Comment: RevTeX file, 26 pages, 3 Postscript figures, uses epsf.sty. submitted
to Phys. Rev.
Study of Warm Electron Injection in Double Gate SONOS by Full Band Monte Carlo Simulation
In this paper we investigate warm electron injection in a double gate SONOS
memory by means of 2D full-band Monte Carlo simulations of the Boltzmann
Transport Equation (BTE). Electrons are accelerated in the channel by a
drain-to-source voltage VDS smaller than 3 V, so that programming occurs via
electrons tunneling through a potential barrier whose height has been
effectively reduced by the accumulated kinetic energy. Particle energy
distribution at the semiconductor/oxide interface is studied for different bias
conditions and different positions along the channel. The gate current is
calculated with a continuum-based post-processing method as a function of the
particle distribution obtained from Monte Carlo. Simulation results show that
the gate current increases by several orders of magnitude with increasing drain
bias and warm electron injection can be an interesting option for programming
when short channel effects prohibit the application of larger drain bias
Enhanced shot noise in resonant tunneling: theory and experiment
We show that shot noise in a resonant tunneling diode biased in the negative
differential resistance regions of the I-V characteristic is enhanced with
respect to ``full'' shot noise. We provide experimental results showing a Fano
factor up to 6.6, and show that it is a dramatic effect caused by
electron-electron interaction through Coulomb force, enhanced by the particular
shape of the density of states in the well. We also present numerical results
from the proposed theory, which are in agreement with the experiment,
demonstrating that the model accounts for the relevant physics involved in the
phenomenon.Comment: 4 pages, 4 figure
Atomistic quantum transport modeling of metal-graphene nanoribbon heterojunctions
We calculate quantum transport for metal-graphene nanoribbon heterojunctions
within the atomistic self-consistent Schr\"odinger/Poisson scheme. Attention is
paid on both the chemical aspects of the interface bonding as well the
one-dimensional electrostatics along the ribbon length. Band-bending and doping
effects strongly influence the transport properties, giving rise to conductance
asymmetries and a selective suppression of the subband formation. Junction
electrostatics and p-type characteristics drive the conduction mechanism in the
case of high work function Au, Pd and Pt electrodes, while contact resistance
becomes dominant in the case of Al.Comment: 4 pages, 5 figure
Operation of Quantum Cellular Automaton cells with more than two electrons
We present evidence that operation of QCA (Quantum Cellular Automaton) cells
with four dots is possible with an occupancy of 4N+2 electrons per cell (N
being an integer). We show that interaction between cells can be described in
terms of a revised formula for cell polarization, which is based only on the
difference between diagonal occupancies. We validate our conjectures with full
quantum simulations of QCA cells for a number of electrons varying from 2 to 6,
using the Configuration-Interaction method.Comment: 4 pages, 4 figures included, submitted to AP
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