997 research outputs found
Further research on high open circuit voltage in silicon solar cells
The results of a new research on the use of controlled dopant profiles and oxide passivation to achieve high open circuit voltage V sub oc in silicon solar cells is presented. Ion implantation has been used to obtain nearly optimal values of surface dopant concentration. The concentrations are selected so as to minimize heavy doping effects and thereby provide both high blue response and high V sub oc ion implantation technique has been successfully applied to fabrication of both n-type and p-type emitters. V sub oc of up to 660 mV is reported and AMO efficiency of 16.1% has been obtained
Processing technology for high efficiency silicon solar cells
Recent advances in silicon solar cell processing have led to attainment of conversion efficiency approaching 20%. The basic cell design is investigated and features of greatest importance to achievement of 20% efficiency are indicated. Experiments to separately optimize high efficiency design features in test structures are discussed. The integration of these features in a high efficiency cell is examined. Ion implantation has been used to achieve optimal concentrations of emitter dopant and junction depth. The optimization reflects the trade-off between high sheet conductivity, necessary for high fill factor, and heavy doping effects, which must be minimized for high open circuit voltage. A second important aspect of the design experiments is the development of a passivation process to minimize front surface recombination velocity. The manner in which a thin SiO2 layer may be used for this purpose is indicated without increasing reflection losses, if the antireflection coating is properly designed. Details are presented of processing intended to reduce recombination at the contact/Si interface. Data on cell performance (including CZ and ribbon) and analysis of loss mechanisms are also presented
Tunnel junctions for InP-on-Si solar cells
Growing, by metalorganic chemical vapor deposition, a tunnel junction is described, which makes possible and ohmic back contact in an n-on-p InP solar cell on a silicon substrate. The junction between heavily doped layers of p-type InGaAs and n-type InP shows resistance low enough not to affect the performance of these cells. InP solar cells made on n-type Si substrates with this structure were measured with an efficiency of 9.9 percent. Controls using p-type GaAs substrates showed no significant difference in cell performance, indicating that the resistance associated with the tunnel junction is less than about 0.1 ohm/sq cm
Intercalated Rare-Earth Metals under Graphene on SiC
Intercalation of rare earth metals ( = Eu, Dy, and Gd) is achieved by
depositing the metal on graphene that is grown on silicon-carbide (SiC)
and by subsequent annealing at high temperatures to promote intercalation. STM
images of the films reveal that the graphene layer is defect free and that each
of the intercalated metals has a distinct nucleation pattern. Intercalated Eu
forms nano-clusters that are situated on the vertices of a Moir{\`e} pattern,
while Dy and Gd form randomly distributed nano-clusters. X-ray magnetic
circular dichroism (XMCD) measurements of intercalated films reveal the
magnetic properties of these 's nano-clusters. Furthermore, field
dependence and temperature dependence of the magnetic moments extracted from
the XMCD show paramagnetic-like behaviors with moments that are generally
smaller than those predicted by the Brillouin function. XMCD measurements of
-oxides compared with those of the intercalated 's under graphene after
exposure to air for months indicate that the graphene membranes protect these
intercalants against oxidation.Comment: 9 pages, 7 figure
Intercalated europium metal in epitaxial graphene on SiC
X-ray magnetic circular dichroism (XMCD) reveal the magnetic properties of
intercalated europium metal under graphene on SiC(0001). Intercalation of Eu
nano-clusters (average size 2.5 nm) between graphene and SiC substate are
formed by deposition of Eu on epitaxially grown graphene that is subsequently
annealed at various temperatures while keeping the integrity of the graphene
layer. Using sum-rules analysis of the XMCD of Eu M edges at
K, our samples show paramagnetic-like behavior with distinct anomaly at T
90 K which may be related to the N{\`e}el transition, T = 91 K,
of bulk metal Eu. We find no evidence of ferromagnetism due to EuO or
antiferromagnetism due to EuO indicating that the graphene layer
protects the intercalated metallic Eu against oxidation over months of exposure
to atmospheric environment.Comment: 6 pages, 5 figure
Non-linear vortex dynamics and transient effects in ferromagnetic disks
We report a time resolved imaging and micromagnetic simulation study of the
relaxation dynamics of a magnetic vortex in the non-linear regime. We use
time-resolved photoemission electron microscopy and micromagnetic calculations
to examine the emergence of non-linear vortex dynamics in patterned Ni80Fe20
disks in the limit of long field pulses. We show for core shifts beyond ~20-25%
of the disk radius, the initial motion is characterized by distortions of the
vortex, a transient cross-tie wall state, and instabilities in the core
polarization that influence the core trajectories.Comment: 11 pages, 3 figures, submitted to Phys. Rev. Let
InP shallow-homojunction solar cells
Indium phosphide solar cells with very thin n-type emitters have been made by both ion implantation and metalorganic chemical vapor deposition. Air mass zero efficiencies as high as 18.8 percent (NASA measurement) have been achieved. Although calculations show that, as is the case with GaAs, a heterostructure is expected to be required for the highest efficiencies attainable, the material properties of InP give the shallow-homojunction structure a greater potential than in the case of GaAs. The best cells, which were those made by ion implantation, show open-circuit voltage (V sub oc) of 873 mV, short-circuit current of 357 A/sq m (35.7 mA/sq cm), and fill factor of 0.829. Improvements are anticipated in all three of these parameters. Internal quantum efficiency peaks at over 90 percent in the red end of the spectrum, but drops to 54 percent in the blue end. Other cells have achieved 74 percent in the blue end. Detailed modeling of the data indicates that a high front surface recombination velocity is responsible for the low blue response, that the carrier lifetime is high enough to allow good carrier collection from both the base and the emitter, and that the voltage is base-limited
Local Environment of Ferromagnetically Ordered Mn in Epitaxial InMnAs
The magnetic properties of the ferromagnetic semiconductor In0.98Mn0.02As
were characterized by x-ray absorption spectroscopy and x-ray magnetic circular
dichroism. The Mn exhibits an atomic-like L2,3 absorption spectrum that
indicates that the 3d states are highly localized. In addition, a large
dichroism at the Mn L2,3 edge was observed from 5-300 K at an applied field of
2T. A calculated spectrum assuming atomic Mn2+ yields the best agreement with
the experimental InMnAs spectrum. A comparison of the dichroism spectra of MnAs
and InMnAs show clear differences suggesting that the ferromagnetism observed
in InMnAs is not due to hexagonal MnAs clusters. The temperature dependence of
the dichroism indicates the presence of two ferromagnetic species, one with a
transition temperature of 30 K and another with a transition temperature in
excess of 300 K. The dichroism spectra are consistent with the assignment of
the low temperature species to random substitutional Mn and the high
temperature species to Mn near-neighbor pairs.Comment: 10 pages, 4 figures, accepted by Applied Physics Letter
Magnetic Vortex Core Dynamics in a Ferromagnetic Dot
We report direct imaging by means of x-ray photoemission electron microscopy
of the dynamics of magnetic vortices confined in micron-size circular Permalloy
dots that are 30 nm thick. The vortex core positions oscillate on a 10-ns
timescale in a self-induced magnetostatic potential well after the in-plane
magnetic field is turned off. The measured oscillation frequencies as a
function of the aspect ratio (thickness/radius) of the dots are in agreement
with theoretical calculations presented for the same geometry.Comment: 18 pages including 4 figure
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