362 research outputs found
Hot-hole lasers in III-V semiconductors
Following the success of p-Ge hot-hole lasers, there is also potential for
using other semiconductor materials, notably III-V's such as GaAs and InSb.
Previous analysis had suggested that a large effective mass ratio between the
heavy and light holes is advantageous, which implies that InSb would make an
excellent hot-hole laser. Using our Monte Carlo simulations of both GaAs and
InSb hot-hole lasers in combination with a rate equation model, we see that
previously accepted criteria used to predict performance are not always
reliable, and we suggest suitable alternatives. The simulation results include
gain and gain bandwidth as a function of field strength and laser frequency,
and alternative field orientations and photon polarizations are considered.
Comparisons are made with bulk p-Ge systems. The optimum conditions predicted
by our simulations could then be used in the design of quantum-well hot-hole
lasers.Comment: 7 pages, 4 figures (8 frames
An optimised algorithm for ionized impurity scattering in Monte Carlo simulations
We present a new optimised model of Brookes-Herring ionized impurity
scattering for use in Monte Carlo simulations of semiconductors. When
implemented, it greatly decreases the execution time needed for simulations
(typically by a factor of the order of 100), and also properly incorporates the
great proportion of small angle scatterings that are neglected in the standard
algorithm. It achieves this performance by using an anisotropic choice of
scattering angle which accurately mimics the true angular distribution of
ionized impurity scattering.Comment: 5 page
Intrinsic spin dynamics in semiconductor quantum dots
We investigate the characteristic spin dynamics corresponding to
semiconductor quantum dots within the multiband envelope function approximation
(EFA). By numerically solving an Hamiltonian we treat
systems based on different III-V semiconductor materials.It is shown that, even
in the absence of an applied magnetic field, these systems show intrinsic spin
dynamics governed by intraband and interband transitions leading to
characteristic spin frequencies ranging from the THz to optical frequencies.Comment: to be published in Nanotechnology. Separated figure file
A multiband envelope function model for quantum transport in a tunneling diode
We present a simple model for electron transport in semiconductor devices
that exhibit tunneling between the conduction and valence bands. The model is
derived within the usual Bloch-Wannier formalism by a k-expansion, and is
formulated in terms of a set of coupled equations for the electron envelope
functions. Its connection with other models present in literature is discussed.
As an application we consider the case of a Resonant Interband Tunneling Diode,
demonstrating the ability of the model to reproduce the expected behaviour of
the current as a function of the applied voltageComment: 8 pages, 4 figure
Two mini-band model for self-sustained oscillations of the current through resonant tunneling semiconductor superlattices
A two miniband model for electron transport in semiconductor superlattices
that includes scattering and interminiband tunnelling is proposed. The model is
formulated in terms of Wigner functions in a basis spanned by Pauli matrices,
includes electron-electron scattering in the Hartree approximation and modified
Bhatnagar-Gross-Krook collision tems. For strong applied fields, balance
equations for the electric field and the miniband populations are derived using
a Chapman-Enskog perturbation technique. These equations are then solved
numerically for a dc voltage biased superlattice. Results include
self-sustained current oscillations due to repeated nucleation of electric
field pulses at the injecting contact region and their motion towards the
collector. Numerical reconstruction of the Wigner functions shows that the
miniband with higher energy is empty during most of the oscillation period: it
becomes populated only when the local electric field (corresponding to the
passing pulse) is sufficiently large to trigger resonant tunneling.Comment: 26 pages, 3 figures, to appear in Phys. Rev.
Rate-dependency of action potential duration and refractoriness in isolated myocytes from the rabbit AV node and atrium
During atrial fibrillation, ventricular rate is determined by atrioventricular nodal (AVN) conduction, which in part is dependent upon the refractoriness of single AVN cells. The aims of this study were to investigate the rate-dependency of the action potential duration (APD) and effective refractory period (ERP) in single myocytes isolated from the AV node and atrium of rabbit hearts, using whole cell patch clamping, and to determine the contribution of the 4-aminopyridine (4-AP)-sensitive current, ITO1to these relationships in the two cell types. AVN cells had a more positive maximum diastolic potential (-60±1 v-71±2 mV), lower Vmax(8±2 v 144±17 V/s) and higher input resistance [420±46 v 65±7 MOHgr (mean±s.eP<0.05n=9–33)], respectively, than atrial myocytes. Stepwise increases in rate from 75 beats/min caused activation failure and Wenckebach periodicity in AVN cells (at around 400 beats/min), but 1:1 activation in atrial cells (at up to 600 beats/min). Rate reduction from 300 to 75 beats/min shortened the ERP in both cell types (from 155±7 to 135±11 ms in AVN cells [P<0.05, n=6] and from 130±8 to 106±7 ms in atrial cells [P<0.05, n=10]). Rate increase from 300 to 480 and 600 beats/min shortened ERP in atrial cells, by 12±4% (n=8) and 26±7% (n=7), respectively (P<0.05). By contrast, AVN ERP did not shorten at rates >300 beats/min. In atrial cells, rate reduction to 75 beats/min caused marked shortening of APD50(from 51±6 to 29±6 ms, P<0.05). 4-AP (1 mm) significantly prolonged atrial APD50at 75 beats/min (P<0.05, n=7), but not at 300 or 400 beats/min. In AVN cells, in contrast, there was less effect of rate change on APD, and 4-AP did not alter APD50at any rate. 4-AP also did not affect APD90or ERP in either cell type. In conclusion, a lack of ERP-shortening at high rates in rabbit single AVN cells may contribute to ventricular rate control. ITO1contributed to the APD50rate relation in atrial, but not AVN cells and did not contribute to the ERP rate relation in either cell type
Analysis of a diffusive effective mass model for nanowires
We propose in this paper to derive and analyze a self-consistent model
describing the diffusive transport in a nanowire. From a physical point of
view, it describes the electron transport in an ultra-scaled confined
structure, taking in account the interactions of charged particles with
phonons. The transport direction is assumed to be large compared to the wire
section and is described by a drift-diffusion equation including effective
quantities computed from a Bloch problem in the crystal lattice. The
electrostatic potential solves a Poisson equation where the particle density
couples on each energy band a two dimensional confinement density with the
monodimensional transport density given by the Boltzmann statistics. On the one
hand, we study the derivation of this Nanowire Drift-Diffusion Poisson model
from a kinetic level description. On the other hand, we present an existence
result for this model in a bounded domain
Evaluation des Behindertengleichstellungsgesetzes: Abschlussbericht
Das Behindertengleichstellungsgesetz (BGG) ist am 1. Mai 2002 in Kraft getreten. Ziel des BGG ist, die Benachteiligung von behinderten Menschen zu beseitigen, ihre gleichberechtigte Teilhabe am Leben in der Gesellschaft zu gewährleisten und ihnen eine selbstbestimmte Lebensführung zu ermöglichen. Kernstück des BGG ist die Barrierefreiheit. Sie ist eine wesentliche Voraussetzung für eine selbstbestimmte und gleichberechtigte Teilhabe. Gut zehn Jahre nach seinem Inkrafttreten war es an der Zeit, das BGG im Rahmen des Nationalen Aktionsplans zur Umsetzung der UN-Behindertenrechtskonvention (UN-BRK) wissenschaftlich auf seine Wirkung zu überprüfen. Im Fokus standen dabei die Fragen, ob alle Gruppen von Menschen mit Behinderungen ausreichend berücksichtigt sind und sich die Instrumente des BGG bewährt haben. Bei der Evaluation waren die Vorgaben der UN-BRK zu berücksichtigen. Die Perspektive von Menschen mit Behinderungen wurde von Anfang an einbezogen
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