203 research outputs found
Is there a linewidth theory for semiconductor lasers?
Semiconductor laser generation begins at a critical injection when the gain
and loss spectra touch each other at a singular frequency. In the framework of
the standard (Schawlow-Townes-Lax-Henry) theory, the finite linewidth results
from the account of fluctuations associated with the random spontaneous
emission processes. This approach is based on the assumption that in the
mean-field approximation the singular frequency generation persists for
injection levels higher than critical. We show that this assumption in the
framework of the Boltzmann kinetic equation for electrons and photons is
invalid and therefore the standard description of semiconductor laser linewidth
lacks theoretical foundation. Experimental support of the standard theory is
also questionable
Quantum confinement corrections to the capacitance of gated one-dimensional nanostructures
With the help of a multi-configurational Green's function approach we
simulate single-electron Coulomb charging effects in gated ultimately scaled
nanostructures which are beyond the scope of a selfconsistent mean-field
description. From the simulated Coulomb-blockade characteristics we derive
effective system capacitances and demonstrate how quantum confinement effects
give rise to corrections. Such deviations are crucial for the interpretation of
experimentally determined capacitances and the extraction of
application-relevant system parameters
Electrically-induced n-i-p junctions in multiple graphene layer structures
The Fermi energies of electrons and holes and their densities in different
graphene layers (GLs) in the n- and p-regions of the electrically induced n-i-p
junctions formed in multiple-GL structures are calculated both numerically and
using a simplified analytical model. The reverse current associated with the
injection of minority carriers through the n- and p-regions in the
electrically-induced n-i-p junctions under the reverse bias is calculated as
well. It is shown that in the electrically-induced n-i-p junctions with
moderate numbers of GLs the reverse current can be substantially suppressed.
Hence, multiple-GL structures with such n-i-p junctions can be used in
different electron and optoelectron devices.Comment: 7 pages, 6 figure
Direct observation of Levy flight of holes in bulk n-InP
We study the photoluminescence spectra excited at an edge side of n-InP slabs
and observed from the broadside. In a moderately doped sample the intensity
drops off as a power-law function of the distance from the excitation - up to
several millimeters - with no change in the spectral shape.The hole
distribution is described by a stationary Levy-flight process over more than
two orders of magnitude in both the distance and hole concentration. For
heavily-doped samples, the power law is truncated by free-carrier absorption.
Our experiments are near-perfectly described by the Biberman-Holstein transport
equation with parameters found from independent optical experiments.Comment: 4 pages, 3 figure
Monte Carlo study of coaxially gated CNTFETs: capacitive effects and dynamic performance
Carbon Nanotube (CNT) appears as a promising candidate to shrink field-effect
transistors (FET) to the nanometer scale. Extensive experimental works have
been performed recently to develop the appropriate technology and to explore DC
characteristics of carbon nanotube field effect transistor (CNTFET). In this
work, we present results of Monte Carlo simulation of a coaxially gated CNTFET
including electron-phonon scattering. Our purpose is to present the intrinsic
transport properties of such material through the evaluation of electron
mean-free-path. To highlight the potential of high performance level of CNTFET,
we then perform a study of DC characteristics and of the impact of capacitive
effects. Finally, we compare the performance of CNTFET with that of Si nanowire
MOSFET.Comment: 15 pages, 14 figures, final version to be published in C. R. Acad.
Sci. Pari
Spin photocurrents and circular photon drag effect in (110)-grown quantum well structures
We report on the study of spin photocurrents in (110)-grown quantum well
structures. Investigated effects comprise the circular photogalvanic effect and
so far not observed circular photon drag effect. The experimental data can be
described by an analytical expression derived from a phenomenological theory. A
microscopic model of the circular photon drag effect is developed demonstrating
that the generated current has spin dependent origin.Comment: 6 pages, 3 figure
Semiconductor High-Energy Radiation Scintillation Detector
We propose a new scintillation-type detector in which high-energy radiation
produces electron-hole pairs in a direct-gap semiconductor material that
subsequently recombine producing infrared light to be registered by a
photo-detector. The key issue is how to make the semiconductor essentially
transparent to its own infrared light, so that photons generated deep inside
the semiconductor could reach its surface without tangible attenuation. We
discuss two ways to accomplish this, one based on doping the semiconductor with
shallow impurities of one polarity type, preferably donors, the other by
heterostructure bandgap engineering. The proposed semiconductor scintillator
combines the best properties of currently existing radiation detectors and can
be used for both simple radiation monitoring, like a Geiger counter, and for
high-resolution spectrography of the high-energy radiation. The most important
advantage of the proposed detector is its fast response time, about 1 ns,
essentially limited only by the recombination time of minority carriers.
Notably, the fast response comes without any degradation in brightness. When
the scintillator is implemented in a qualified semiconductor material (such as
InP or GaAs), the photo-detector and associated circuits can be epitaxially
integrated on the scintillator slab and the structure can be stacked-up to
achieve virtually any desired absorption capability
Random Sequential Adsorption: From Continuum to Lattice and Pre-Patterned Substrates
The random sequential adsorption (RSA) model has served as a paradigm for
diverse phenomena in physical chemistry, as well as in other areas such as
biology, ecology, and sociology. In the present work, we survey aspects of the
RSA model with emphasis on the approach to and properties of jammed states
obtained for large times in continuum deposition versus that on lattice
substrates, and on pre-patterned surfaces. The latter model has been of recent
interest in the context of efforts to use pre-patterning as a tool to improve
selfassembly in micro- and nanoscale surface structure engineering
A Unified Model for Two Localisation Problems: Electron States in Spin-Degenerate Landau Levels, and in a Random Magnetic Field
A single model is presented which represents both of the two apparently
unrelated localisation problems of the title. The phase diagram of this model
is examined using scaling ideas and numerical simulations. It is argued that
the localisation length in a spin-degenerate Landau level diverges at two
distinct energies, with the same critical behaviour as in a spin-split Landau
level, and that all states of a charged particle moving in two dimensions, in a
random magnetic field with zero average, are localised.Comment: 7 pages (RevTeX 3.0) plus 4 postscript figure
- …