2,009 research outputs found
Minority carrier diffusion lengths and mobilities in low-doped n-InGaAs for focal plane array applications
The hole diffusion length in n-InGaAs is extracted for two samples of
different doping concentrations using a set of long and thin diffused junction
diodes separated by various distances on the order of the diffusion length. The
methodology is described, including the ensuing analysis which yields diffusion
lengths between 70 - 85 um at room temperature for doping concentrations in the
range of 5 - 9 x 10^15 cm-3. The analysis also provides insight into the
minority carrier mobility which is a parameter not commonly reported in the
literature. Hole mobilities on the order of 500 - 750 cm2/Vs are reported for
the aforementioned doping range, which are comparable albeit longer than the
majority hole mobility for the same doping magnitude in p-InGaAs. A radiative
recombination coefficient of (0.5-0.2)x10^-10 cm^-3s^-1 is also extracted from
the ensuing analysis for an InGaAs thickness of 2.7 um. Preliminary evidence is
also given for both heavy and light hole diffusion. The dark current of
InP/InGaAs p-i-n photodetectors with 25 and 15 um pitches are then calibrated
to device simulations and correlated to the extracted diffusion lengths and
doping concentrations. An effective Shockley-Read-Hall lifetime of between
90-200 us provides the best fit to the dark current of these structures.Comment: 9 pages, 5 figure
Heavy and light hole minority carrier transport properties in low-doped n-InGaAs lattice matched to InP
Minority carrier diffusion lengths in low-doped n-InGaAs using InP/InGaAs
double-heterostructures are reported using a simple electrical technique. The
contributions from heavy and light holes are also extracted using this
methodology, including minority carrier mobilities and lifetimes. Heavy holes
are shown to initially dominate the transport due to their higher valence band
density of states, but at large diffusion distances, the light holes begin to
dominate due to their larger diffusion length. It is found that heavy holes
have a diffusion length of 54.5 +/- 0.6 microns for an n-InGaAs doping of 8.4 x
10^15 cm-3 at room temperature, whereas light holes have a diffusion length in
excess of 140 microns. Heavy holes demonstrate a mobility of 692 +/- 63 cm2/Vs
and a lifetime of 1.7 +/- 0.2 microsec, whereas light holes demonstrate a
mobility of 6200 +/- 960 cm-2/Vs and a slightly longer lifetime of 2.6 +/- 1.0
microsec. The presented method, which is limited to low injection conditions,
is capable of accurately resolving minority carrier transport properties.Comment: 16 pages, 13 figure
Terahertz frequency-wavelet domain deconvolution for stratigraphic and subsurface investigation of art painting
Terahertz frequency-wavelet deconvolution is utilized specifically for the stratigraphic and subsurface investigation of art paintings with terahertz reflective imaging. In order to resolve the optically thin paint layers, a deconvolution technique is enhanced by the combination of frequency-domain filtering and stationary wavelet shrinkage, and applied to investigate a mid-20th century Italian oil painting on paperboard, After Fishing, by Ausonio Tanda. Based on the deconvolved terahertz data, the stratigraphy of the painting including the paint layers is reconstructed and subsurface features are clearly revealed, demonstrating that terahertz frequencywavelet deconvolution can be an effective tool to characterize stratified systems with optically thin layers
One of the closest exoplanet pairs to the 3:2 Mean Motion Resonance: K2-19b \& c
The K2 mission has recently begun to discover new and diverse planetary
systems. In December 2014 Campaign 1 data from the mission was released,
providing high-precision photometry for ~22000 objects over an 80 day timespan.
We searched these data with the aim of detecting further important new objects.
Our search through two separate pipelines led to the independent discovery of
K2-19b \& c, a two-planet system of Neptune sized objects (4.2 and 7.2
), orbiting a K dwarf extremely close to the 3:2 mean motion
resonance. The two planets each show transits, sometimes simultaneously due to
their proximity to resonance and alignment of conjunctions. We obtain further
ground based photometry of the larger planet with the NITES telescope,
demonstrating the presence of large transit timing variations (TTVs), and use
the observed TTVs to place mass constraints on the transiting objects under the
hypothesis that the objects are near but not in resonance. We then
statistically validate the planets through the \texttt{PASTIS} tool,
independently of the TTV analysis.Comment: 18 pages, 10 figures, accepted to A&A, updated to match published
versio
Observation of the antimatter helium-4 nucleus
High-energy nuclear collisions create an energy density similar to that of
the universe microseconds after the Big Bang, and in both cases, matter and
antimatter are formed with comparable abundance. However, the relatively
short-lived expansion in nuclear collisions allows antimatter to decouple
quickly from matter, and avoid annihilation. Thus, a high energy accelerator of
heavy nuclei is an efficient means of producing and studying antimatter. The
antimatter helium-4 nucleus (), also known as the anti-{\alpha}
(), consists of two antiprotons and two antineutrons (baryon
number B=-4). It has not been observed previously, although the {\alpha}
particle was identified a century ago by Rutherford and is present in cosmic
radiation at the 10% level. Antimatter nuclei with B < -1 have been observed
only as rare products of interactions at particle accelerators, where the rate
of antinucleus production in high-energy collisions decreases by about 1000
with each additional antinucleon. We present the observation of the antimatter
helium-4 nucleus, the heaviest observed antinucleus. In total 18
counts were detected at the STAR experiment at RHIC in 10 recorded Au+Au
collisions at center-of-mass energies of 200 GeV and 62 GeV per nucleon-nucleon
pair. The yield is consistent with expectations from thermodynamic and
coalescent nucleosynthesis models, which has implications beyond nuclear
physics.Comment: 19 pages, 4 figures. Submitted to Nature. Under media embarg
Strangeness Enhancement in Cu+Cu and Au+Au Collisions at \sqrt{s_{NN}} = 200 GeV
We report new STAR measurements of mid-rapidity yields for the ,
, , , , ,
particles in Cu+Cu collisions at \sNN{200}, and mid-rapidity
yields for the , , particles in Au+Au at
\sNN{200}. We show that at a given number of participating nucleons, the
production of strange hadrons is higher in Cu+Cu collisions than in Au+Au
collisions at the same center-of-mass energy. We find that aspects of the
enhancement factors for all particles can be described by a parameterization
based on the fraction of participants that undergo multiple collisions
Growth of Long Range Forward-Backward Multiplicity Correlations with Centrality in Au+Au Collisions at = 200 GeV
Forward-backward multiplicity correlation strengths have been measured with
the STAR detector for Au+Au and collisions at =
200 GeV. Strong short and long range correlations (LRC) are seen in central
Au+Au collisions. The magnitude of these correlations decrease with decreasing
centrality until only short range correlations are observed in peripheral Au+Au
collisions. Both the Dual Parton Model (DPM) and the Color Glass Condensate
(CGC) predict the existence of the long range correlations. In the DPM the
fluctuation in the number of elementary (parton) inelastic collisions produces
the LRC. In the CGC longitudinal color flux tubes generate the LRC. The data is
in qualitative agreement with the predictions from the DPM and indicates the
presence of multiple parton interactions.Comment: 6 pages, 3 figures The abstract has been slightly modifie
Longitudinal Spin Transfer to and Hyperons in Polarized Proton-Proton Collisions at = 200 GeV
The longitudinal spin transfer, , from high energy polarized protons
to and hyperons has been measured for the first time
in proton-proton collisions at with the STAR
detector at RHIC. The measurements cover pseudorapidity, , in the range
and transverse momenta, , up to . The longitudinal spin transfer is found to be for inclusive
and for
inclusive hyperons with and . The dependence on and is presented.Comment: 5 pages, 4 figure
K/pi Fluctuations at Relativistic Energies
We report results for fluctuations from Au+Au collisions at
= 19.6, 62.4, 130, and 200 GeV using the STAR detector at the
Relativistic Heavy Ion Collider. Our results for fluctuations in
central collisions show little dependence on the incident energies studied and
are on the same order as results observed by NA49 at the Super Proton
Synchrotron in central Pb+Pb collisions at = 12.3 and 17.3 GeV.
We also report results for the collision centrality dependence of
fluctuations as well as results for , ,
, and fluctuations. We observe that the
fluctuations scale with the multiplicity density, , rather than the
number of participating nucleons.Comment: 6 pages, 4 figure
The Close Binary Fraction as a Function of Stellar Parameters in APOGEE:A Strong Anti-Correlation With α Abundances
We use observations from the APOGEE survey to explore the relationship
between stellar parameters and multiplicity. We combine high-resolution repeat
spectroscopy for 41,363 dwarf and subgiant stars with abundance measurements
from the APOGEE pipeline and distances and stellar parameters derived using
\textit{Gaia} DR2 parallaxes from \cite{Sanders2018} to identify and
characterise stellar multiples with periods below 30 years, corresponding to
\drvm 3 \kms, where \drvm\ is the maximum APOGEE-detected shift in the
radial velocities. Chemical composition is responsible for most of the
variation in the close binary fraction in our sample, with stellar parameters
like mass and age playing a secondary role. In addition to the previously
identified strong anti-correlation between the close binary fraction and \feh\,
we find that high abundances of elements also suppress multiplicity at
most values of \feh\ sampled by APOGEE. The anti-correlation between
abundances and multiplicity is substantially steeper than that observed for Fe,
suggesting C, O, and Si in the form of dust and ices dominate the opacity of
primordial protostellar disks and their propensity for fragmentation via
gravitational stability. Near \feh{} = 0 dex, the bias-corrected close binary
fraction ( au) decreases from 100 per cent at \alh{} = 0.2
dex to 15 per cent near \alh{} = 0.08 dex, with a suggestive turn-up
to 20 per cent near \alh{} = 0.2. We conclude that the relationship
between stellar multiplicity and chemical composition for sun-like dwarf stars
in the field of the Milky Way is complex, and that this complexity should be
accounted for in future studies of interacting binaries.Comment: 15 pages, 10 figures, plus appendices; accepted to MNRA
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