305 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 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
Induced Ge Spin Polarization at the Fe/Ge Interface
We report direct experimental evidence showing induced magnetic moments on Ge
at the interface in an Fe/Ge system. Details of the x-ray magnetic circular
dichroism and resonant magnetic scattering at the Ge L edge demonstrate the
presence of spin-polarized {\it s} states at the Fermi level, as well as {\it
d} character moments at higher energy, which are both oriented antiparallel to
the moment of the Fe layer. Use of the sum rules enables extraction of the L/S
ratio, which is zero for the {\it s} part and for the {\it d}
component. These results are consistent with layer-resolved electronic
structure calculations, which estimate the {\it s} and {\it d} components of
the Ge moment are anti-parallel to the Fe {\it 3d} moment and have a magnitude
of .Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Room-temperature multiferroic hexagonal LuFeO films
The crystal and magnetic structures of single-crystalline hexagonal LuFeO
films have been studied using x-ray, electron and neutron diffraction methods.
The polar structure of these films are found to persist up to 1050 K; and the
switchability of the polar behavior is observed at room temperature, indicating
ferroelectricity. An antiferromagnetic order was shown to occur below 440 K,
followed by a spin reorientation resulting in a weak ferromagnetic order below
130 K. This observation of coexisting multiple ferroic orders demonstrates that
hexagonal LuFeO films are room-temperature multiferroics
Layer resolved magnetic domain imaging of epitaxial heterostructures in large applied magnetic fields
We use X-ray Excited Luminescence Microscopy to investigate the elemental and layer resolved magnetic reversal in an interlayer exchange coupled (IEC) epitaxial Fe/Cr wedge/Co heterostructure. The transition from strongly coupled parallel Co-Fe reversal for Cr thickness tCr < 0.34 nm to weakly coupled layer independent reversal for tCr > 1.5 nm is punctuated at 0.34 < tCr < 1.5 nm by a combination of IEC guided domain wall motion and stationary zig zag domain walls. Domain walls nucleated at switching field minima are guided by IEC spatial gradients and collapse at switching field maxima.RM acknowledges funding from the European Community under the Seventh Framework Program
Contract No. 247368: 3SPIN. DL acknowledges funding from the EPSRC. The work performed at the Advanced
Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy
Sciences under Contract No. DE-AC02-06CH11357.This is the accepted manuscript. The final version is available at http://scitation.aip.org/content/aip/journal/apl/106/7/10.1063/1.4913359
Growth Diagram and Magnetic Properties of Hexagonal LuFe2O4 Thin Films
A growth diagram of Lu-Fe-O compounds on MgO(111) substrates using pulsed laser deposition is constructed based on extensive growth experiments. The LuFe2O4 phase can only be grown in a small range of temperature and O2 pressure conditions. An understanding of the growth mechanism of Lu-Fe-O compound films is offered in terms of the thermochemistry at the surface. Superparamagnetism is observed in the LuFe2O4 film and is explained in terms of the effect of the impurity hexagonal LuFeO3 (h-LuFeO3) phase and structural defects
Growth diagram and magnetic properties of hexagonal LuFe2O4 thin films
Agrowth diagram of Lu-Fe-O compounds on MgO (111) substrates using pulsed laser deposition is constructed based on extensive growth experiments. The LuFe2O4 phase can only be grown in a small range of temperature and O2 pressure conditions. An understanding of the growth mechanism of Lu-Fe-O compound films is offered in terms of the thermochemistry at the surface. Superparamagnetism is observed in the LuFe2O4 film and is explained in terms of the effect of the impurity hexagonal LuFeO3 (h-LuFeO3) phase and structural defects
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