61 research outputs found
Optical Spin Orientation in Strained Superlattices
Optical orientation in the strained semiconductor superlattices is
investigated theoretically. The dependence of the features in spin-polarization
spectra on the structure parameters is clarified. The value of polarization in
the first polarization maximum in the SL structures is shown to grow with the
splitting between the hh- and lh- states of the valence band, the joint strain
and confinement effects on the hh1- lh1 splitting being strongly influenced by
the tunneling in the barriers. In strained structures with high barriers for
the holes initial polarization can exceed 95 %. Calculated polarization spectra
are close to the experimental spectra of polarized electron emission.Comment: 20 pages, 8 figure
Fluctuations of the partial filling factors in competitive RSA from binary mixtures
Competitive random sequential adsorption on a line from a binary mix of
incident particles is studied using both an analytic recursive approach and
Monte Carlo simulations. We find a strong correlation between the small and the
large particle distributions so that while both partial contributions to the
fill factor fluctuate widely, the variance of the total fill factor remains
relatively small. The variances of partial contributions themselves are quite
different between the smaller and the larger particles, with the larger
particle distribution being more correlated. The disparity in fluctuations of
partial fill factors increases with the particle size ratio. The additional
variance in the partial contribution of smaller particle originates from the
fluctuations in the size of gaps between larger particles. We discuss the
implications of our results to semiconductor high-energy gamma detectors where
the detector energy resolution is controlled by correlations in the cascade
energy branching process.Comment: 19 pages, 8 figure
Random sequential adsorption of shrinking or spreading particles
We present a model of one-dimensional irreversible adsorption in which
particles once adsorbed immediately shrink to a smaller size or expand to a
larger size. Exact solutions for the fill factor and the particle number
variance as a function of the size change are obtained. Results are compared
with approximate analytical solutions.Comment: 9 pages, 8 figure
Strain-Compensated AlInGaAs-GaAsP Superlattices for Highly-Polarized Electron Emission
Spin-polarized electron emission from the first superlattice photocathodes
developed with strain compensation is investigated. An opposite strain in the
quantum well and barrier layers is complished using an InAlGaAs/GaAsP
superlattice structure. The measured values of maximum polarization and quantum
yield for the structure with a 0.18 um-thick working layer are close to the
best results reported for any strained superlattice photocathode structure,
demonstrating the high potential of strain compensation for future photocathode
applications. An analysis of the photoemission spectra is used to estimate the
parameters responsible for the polarization losses.Comment: 10 pages, 2 figure
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
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
Plasmonic mediated nucleation of resonant nano-cavities in metallic layers
We predict plasmonic mediated nucleation of pancake shaped resonant
nano-cavities in metallic layers that are penetrable to laser fields. The
underlying physics is that the cavity provides a narrow plasmonic resonance
that maximizes its polarizability in an external field. The resonance yields a
significant energy gain making the formation of such cavities highly favorable.
Possible implications include nano-optics and generation of the dielectric bits
in conductive films that underlie the existing optical recording phase change
technology.Comment: 4 pages, 3 figure
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