232 research outputs found
Notes prises de Moroundava à Tsimanandrafouzana : cahier no 13 des notes manuscrites d'Alfred Grandidier
Simulations of solar cell absorption enhancement using resonant modes of a nanosphere array
We propose an approach for enhancing the absorption of thin-film amorphous silicon solar cells using periodic arrangements of resonant dielectric nanospheres deposited as a continuous film on top of a thin planar cell. We numerically demonstrate this enhancement using 3D full field finite difference time domain simulations and 3D finite element device physics simulations of a nanosphere array above a thin-film amorphous silicon solar cell structure featuring back reflector and anti-reflection coating. In addition, we use the full field finite difference time domain results as input to finite element device physics simulations to demonstrate that the enhanced absorption contributes to the current extracted from the device. We study the influence of a multi-sized array of spheres, compare spheres and domes and propose an analytical model based on the temporal coupled mode theory
Efficient Coupling between Dielectric-Loaded Plasmonic and Silicon Photonic Waveguides
The realization of practical on-chip plasmonic devices will require efficient coupling of light into and out of surface plasmon waveguides over short length scales. In this letter, we report on low insertion loss for polymer-on-gold dielectric-loaded plasmonic waveguides end-coupled to silicon-on-insulator waveguides with a coupling efficiency of 79 ± 2% per transition at telecommunication wavelengths. Propagation loss is determined independently of insertion loss by measuring the transmission through plasmonic waveguides of varying length, and we find a characteristic surface-plasmon propagation length of 51 ± 4 μm at a free-space wavelength of λ = 1550 nm. We also demonstrate efficient coupling to whispering-gallery modes in plasmonic ring resonators with an average bending-loss-limited quality factor of 180 ± 8
Efficient Coupling between Dielectric-Loaded Plasmonic and Silicon Photonic Waveguides
Nano-probing station incorporating MEMS probes for 1D device RF on-wafer characterization
International audienc
Solar cell efficiency enhancement via light trapping in printable resonant dielectric nanosphere arrays
Resonant dielectric structures are a promising platform for addressing the key challenge of light trapping in thin-film solar cells. We experimentally and theoretically demonstrate efficiency enhancements in solar cells from dielectric nanosphere arrays. Two distinct amorphous silicon photovoltaic architectures were improved using this versatile light-trapping platform. In one structure, the colloidal monolayer couples light into the absorber in the near-field acting as a photonic crystal light-trapping element. In the other, it acts in the far-field as a graded index antireflection coating to further improve a cell which already included a state-of-the-art random light-trapping texture to achieve a conversion efficiency over 11%. For the near-field flat cell architecture, we directly fabricated the colloidal monolayer on the device through Langmuir–Blodgett deposition in a scalable process that does not degrade the active material. In addition, we present a novel transfer printing method, which utilizes chemical crosslinking of an optically thin adhesion layer to tether sphere arrays to the device surface. The minimally invasive processing conditions of this transfer method enable the application to a wide range of solar cells and other optoelectronic devices.
False-color SEM image of an amorphous silicon solar cell with resonant spheres on top
Photoemission studies of GaMnAs: Mn-concentration dependent properties
Using angle-resolved photoemission, we have investigated the development of
the electronic structure and the Fermi level pinnning in GaMnAs
with Mn concentrations in the range 1--6%. We find that the Mn-induced changes
in the valence-band spectra depend strongly on the Mn concentration, suggesting
that the interaction between the Mn ions is more complex than assumed in
earlier studies. The relative position of the Fermi level is also found to be
concentration-dependent. In particular we find that for concentrations around
3.5--5% it is located very close to the valence-band maximum, which is in the
range where metallic conductivity has been reported in earlier studies. For
concentration outside this range, larger as well as smaller, the Fermi level is
found to be pinned at about 0.15 eV higher energy.Comment: REVTeX style; 7 pages, 3 figure
Spin Waves in Disordered III-V Diluted Magnetic Semiconductors
We propose a new scheme for numerically computing collective-mode spectra for
large-size systems, using a reformulation of the Random Phase Approximation. In
this study, we apply this method to investigate the spectrum and nature of the
spin-waves of a (III,Mn)V Diluted Magnetic Semiconductor. We use an impurity
band picture to describe the interaction of the charge carriers with the local
Mn spins. The spin-wave spectrum is shown to depend sensitively on the
positional disorder of the Mn atoms inside the host semiconductor. Both
localized and extended spin-wave modes are found. Unusual spin and charge
transport is implied.Comment: 14 pages, including 11 figure
Electron transport via local polarons at interface atoms
Electronic transport is profoundly modified in the presence of strong electron-vibration coupling. We show that in certain situations, the electron flow takes place only when vibrations are excited. By controlling the segregation of boron in semiconducting Si(111)-3√×3√R30° surfaces, we create a type of adatom with a dangling-bond state that is electronically decoupled from any other electronic state. However, probing this state with scanning tunnelling microscopy at 5 K yields high currents. These findings are rationalized by ab-initio calculations that show the formation of a local polaron in the transport process
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