2,819 research outputs found
Current and noise correlations in a double dot Cooper pair beam splitter
We consider a double quantum dot coupled to two normal leads and one
superconducting lead, modeling the Cooper pair beam splitter studied in two
recent experiments. Starting from a microscopic Hamiltonian we derive a general
expression for the branching current and the noise crossed correlations in
terms of single and two-particle Green's function of the dot electrons. We then
study numerically how these quantities depend on the energy configuration of
the dots and the presence of direct tunneling between them, isolating the
various processes which come into play. In absence of direct tunneling, the
antisymmetric case (the two levels have opposite energies with respect to the
superconducting chemical potential) optimizes the Crossed Andreev Reflection
(CAR) process while the symmetric case (the two levels have the same energies)
favors the Elastic Cotunneling (EC) process. Switching on the direct tunneling
tends to suppress the CAR process, leading to negative noise crossed
correlations over the whole voltage range for large enough direct tunneling
Thermoelectric effects of an Aharonov-Bohm interferometer with an embedded quantum dot in the Kondo regime
Thermoelectric effects are studied in an Aharonov-Bohm (AB) interferometer
with an embedded quantum dot in the Kondo regime. The AB flux-dependent
transmission probability has an asymmetrical shape arising from the Fano
interference between the direct tunneling path and the Kondo-resonant tunneling
path through a quantum dot. The sign and magnitude of thermopower can be
modulated by the AB flux and the direct tunneling amplitude. In addition, the
thermopower is anomalously enhanced by the Kondo correlation in the quantum dot
near the Kondo temperature (). The Kondo correlation in the quantum dot
also leads to crossover behavior in diagonal transport coefficients as a
function of temperature. The amplitude of an AB oscillation in electric and
thermal conductances is small at temperatures far above , but becomes
enhanced as the system is cooled below . The AB oscillation is strong in
the thermopower and Lorenz number within the crossover region near the Kondo
temperature.Comment: 16 pages, 10 figure
Effects of neglecting carrier tunneling on electrostatic potential in calculating direct tunneling gate current in deep submicron MOSFETs
We investigate the validity of the assumption of neglecting carrier tunneling effects on self-consistent electrostatic potential in calculating direct tunneling gate current in deep submicron MOSFETs. Comparison between simulated and experimental results shows that for accurate modeling of direct tunneling current, tunneling effects on potential profile need to be considered. The relative error in gate current due to neglecting carrier tunneling is higher at higher gate voltages and increases with decreasing oxide thickness. We also study the direct tunneling gate current in MOSFETs with high- gate dielectrics
In_xGa_{1-x}Sb MOSFET: Performance Analysis by Self Consistent CV Characterization and Direct Tunneling Gate Leakage Current
In this paper, Capacitance-Voltage (C-V) characteristics and direct tunneling
(DT) gate leakage current of antimonide based surface channel MOSFET were
investigated. Self-consistent method was applied by solving coupled
Schr\"odinger-Poisson equation taking wave function penetration and strain
effects into account. Experimental I-V and gate leakage characteristic for
p-channel InxGa1-xSb MOSFETs are available in recent literature. However, a
self- consistent simulation of C-V characterization and direct tunneling gate
leakage current is yet to be done for both n- channel and p-channel InxGa1-xSb
surface channel MOSFETs. We studied the variation of C-V characteristics and
gate leakage current with some important process parameters like oxide
thickness, channel composition, channel thickness and temperature for n-channel
MOSFET in this work. Device performance should improve as compressive strain
increases in channel. Our simulation results validate this phenomenon as
ballistic current increases and gate leakage current decreases with the
increase in compressive strain. We also compared the device performance by
replacing InxGa1-xSb with InxGa1-xAs in channel of the structure. Simulation
results show that performance is much better with this replacement.Comment: 7 pages, EIT 2012 IUPUI conferenc
Direct tunneling through high- amorphous HfO: effects of chemical modification
We report first principles modeling of quantum tunneling through amorphous
HfO dielectric layer of metal-oxide-semiconductor (MOS) nanostructures in
the form of n-Si/HfO/Al. In particular we predict that chemically modifying
the amorphous HfO barrier by doping N and Al atoms in the middle region -
far from the two interfaces of the MOS structure, can reduce the
gate-to-channel tunnel leakage by more than one order of magnitude. Several
other types of modification are found to enhance tunneling or induce
substantial band bending in the Si, both are not desired from leakage point of
view. By analyzing transmission coefficients and projected density of states,
the microscopic physics of electron traversing the tunnel barrier with or
without impurity atoms in the high- dielectric is revealed.Comment: 5 pages, 5 figure
Numerical studies of tunneling in a nonharmonic time-dependent potential
Azbel' has recently carried out a WKB-analysis of the effects of a
nonharmonic time-dependent perturbation embedded in an opaque potential
barrier. He suggests the existence of three different transmission regimes:
direct tunneling, activation assisted tunneling, and elevator resonant
activation. We address the same problem with a numerical technique, and find
qualitative agreement with Azbel's picture.Comment: LaTeX document, 15 pages. 4 figures (Fig. 2 comes in 7 pages) in
postscript appended to the LaTeX documen
Trap-Assisted Tunneling in the Schottky Barrier
The paper presents a new way how to calculate the currents in a Schottky barrier. The novel phenomeno-logical model extends the Shockley-Read-Hall recombi-nation-generation theory of trap-assisted tunneling. The proposed approach explains the occurrence of large leakage currents in Schottky structures on wide band semi-conductors with a high Schottky barrier (above 1 eV) and with a high density of traps. Under certain conditions, trap-assisted tunneling (TAT) plays a more important role than direct tunneling
Nonlinear spin-polarized transport through a ferromagnetic domain wall
A domain wall separating two oppositely magnetized regions in a ferromagnetic
semiconductor exhibits, under appropriate conditions, strongly nonlinear I-V
characteristics similar to those of a p-n diode. We study these characteristics
as functions of wall width and temperature. As the width increases or the
temperature decreases, direct tunneling between the majority spin bands
decreases the effectiveness of the diode. This has important implications for
the zero-field quenched resistance of magnetic semiconductors and for the
design of a recently proposed spin transistor.Comment: 5 pages, 3 figure
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