1,173 research outputs found
Design approaches and materials processes for ultrahigh efficiency lattice mismatched multi-junction solar cells
In this study, we report synthesis of large area
(>2cm^2), crack-free GaAs and GaInP double
heterostructures grown in a multi-junction solar cell-like
structure by MOCVD. Initial solar cell data are also
reported for GaInP top cells. These samples were grown
on Ge/Si templates fabricated using wafer bonding and ion
implantation induced layer transfer techniques. The double
heterostructures exhibit radiative emission with uniform
intensity and wavelength in regions not containing
interfacial bubble defects. The minority carrier lifetime of
~1ns was estimated from photoluminescence decay
measurements in both double heterostructures.
We also report on the structural characteristics of
heterostructures, determined via atomic force microscopy
and transmission electron microscopy, and correlate these
characteristics to the spatial variation of the minority
carrier lifetime
Wide-band-gap InAlAs solar cell for an alternative multijunction approach
We have fabricated an In_(0.52)Al_(0.48)As solar cell lattice-matched to InP with efficiency higher than 14% and maximum external quantum efficiency equal to 81%. High quality, dislocation-free In_xAl_(1−x)As alloyed layers were used to fabricate the single junction solar cell. Photoluminescence of In_xAl_(1−x)As showed good material quality and lifetime of over 200 ps. A high band gap In_(0.35)Al_(0.65)As window was used to increase light absorption within the p-n absorber layer and improve cell efficiency, despite strain. The InAlAs top cell reported here is a key building block for an InP-based three junction high efficiency solar cell consisting of InAlAs/InGaAsP/InGaAs lattice-matched to the substrate
Zooming into local active galactic nuclei: The power of combining SDSS-IV MaNGA with higher resolution integral field unit observations
Ionised gas outflows driven by active galactic nuclei (AGN) are ubiquitous in
high luminosity AGN with outflow speeds apparently correlated with the total
bolometric luminosity of the AGN. This empirical relation and theoretical work
suggest that in the range L_bol ~ 10^43-45 erg/s there must exist a threshold
luminosity above which the AGN becomes powerful enough to launch winds that
will be able to escape the galaxy potential. In this paper, we present pilot
observations of two AGN in this transitional range that were taken with the
Gemini North Multi-Object Spectrograph Integral Field Unit (IFU). Both sources
have also previously been observed within the Sloan Digital Sky Survey-IV
(SDSS) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey.
While the MaNGA IFU maps probe the gas fields on galaxy-wide scales and show
that some regions are dominated by AGN ionization, the new Gemini IFU data zoom
into the centre with four times better spatial resolution. In the object with
the lower L_bol we find evidence of a young or stalled biconical AGN-driven
outflow where none was obvious at the MaNGA resolution. In the object with the
higher L_bol we trace the large-scale biconical outflow into the nuclear region
and connect the outflow from small to large scales. These observations suggest
that AGN luminosity and galaxy potential are crucial in shaping wind launching
and propagation in low-luminosity AGN. The transition from small and young
outflows to galaxy-wide feedback can only be understood by combining
large-scale IFU data that trace the galaxy velocity field with higher
resolution, small scale IFU maps.Comment: 14 pages, accepted for publication in MNRA
The Data Analysis Pipeline for the SDSS-IV MaNGA IFU Galaxy Survey: Emission-Line Modeling
SDSS-IV MaNGA (Mapping Nearby Galaxies at Apache Point Observatory) is the
largest integral-field spectroscopy survey to date, aiming to observe a
statistically representative sample of 10,000 low-redshift galaxies. In this
paper we study the reliability of the emission-line fluxes and kinematic
properties derived by the MaNGA Data Analysis Pipeline (DAP). We describe the
algorithmic choices made in the DAP with regards to measuring emission-line
properties, and the effect of our adopted strategy of simultaneously fitting
the continuum and line emission. The effect of random errors are quantified by
studying various fit-quality metrics, idealized recovery simulations and repeat
observations. This analysis demonstrates that the emission lines are well-fit
in the vast majority of the MaNGA dataset and the derived fluxes and errors are
statistically robust. The systematic uncertainty on emission-line properties
introduced by the choice of continuum templates is also discussed. In
particular, we test the effect of using different stellar libraries and simple
stellar-population models on the derived emission-line fluxes and the effect of
introducing different tying prescriptions for the emission-line kinematics. We
show that these effects can generate large ( 0.2 dex) discrepancies at low
signal-to-noise and for lines with low equivalent width (EW); however, the
combined effect is noticeable even for H EW 6~\AA. We provide
suggestions for optimal use of the data provided by SDSS data release 15 and
propose refinements on the \DAP\ for future MaNGA data releases.Comment: accepted on A
Towards an optimized all lattice-matched InAlAs/InGaAsP/InGaAs multijunction solar cell with efficiency >50%
An approach for an all lattice-matched multijunction solar cell optimized design is presented with 5.807 Å lattice constant, together with a detailed analysis of its performance by means of full device modeling. The simulations show that a (1.93 eV)In_(0.37)Al_(0.63)As/(1.39 eV)In_(0.38)Ga_(0.62)As_(0.57)P_(0.43)/(0.94 eV)In_(0.38)Ga_(0.62)As 3-junction solar cell can achieve efficiencies >51% under 100-suns illumination (with V_(oc) = 3.34 V). As a key proof of concept, an equivalent 3-junction solar cell lattice-matched to InP was fabricated and tested. The independently connected single junction solar cells were also tested in a spectrum splitting configuration, showing similar performance to a monolithic tandem device, with V_(oc) = 1.8 V
Ponderomotive Control of Quantum Macroscopic Coherence
It is shown that because of the radiation pressure a Schr\"odinger cat state
can be generated in a resonator with oscillating wall. The optomechanical
control of quantum macroscopic coherence and its detection is taken into
account introducing new cat states. The effects due to the environmental
couplings with this nonlinear system are considered developing an operator
perturbation procedure to solve the master equation for the field mode density
operator.Comment: Latex,22 pages,accepted by Phys.Rev.
Emission-Line Galaxy Surveys as Probes of the Spatial Distribution of Dwarf Galaxies. I. The University of Michigan Survey
Objective-prism surveys which select galaxies on the basis of line-emission
are extremely effective at detecting low-luminosity galaxies and constitute
some of the deepest available samples of dwarfs. In this study, we confirm that
emission-line galaxies (ELGs) in the University of Michigan (UM)
objective-prism survey (MacAlpine et al. 1977-1981) are reliable tracers of
large-scale structure, and utilize the depth of the samples to examine the
spatial distribution of low-luminosity (M -18.0) dwarfs relative to
higher luminosity giant galaxies (M -18.0) in the Updated Zwicky
Catalogue (Falco et al. 1999). New spectroscopic data are presented for 26 UM
survey objects. We analyze the relative clustering properties of the overall
starbursting ELG and normal galaxy populations, using nearest neighbor and
correlation function statistics. This allows us to determine whether the
activity in ELGs is primarily caused by gravitational interactions. We conclude
that galaxy-galaxy encounters are not the sole cause of activity in ELGs since
ELGs tend to be more isolated and are more often found in the voids when
compared to their normal galaxy counterparts. Furthermore, statistical analyses
performed on low-luminosity dwarf ELGs show that the dwarfs are less clustered
when compared to their non-active giant neighbors. The UM dwarf samples have
greater percentages of nearest neighbor separations at large values and lower
correlation function amplitudes relative to the UZC giant galaxy samples. These
results are consistent with the expectations of galaxy biasing.Comment: 17 pages, 4 tables, 10 figures. Accepted for publication in the Ap
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