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  • 1
    Electronic Resource
    Electronic Resource
    Tensile strength of synthetic chemical-vapor-deposited diamond (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5177-5179 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pressure burst tests gave measured tensile strengths between 230 and 410 MPa for a total of six chemical-vapor-deposited (CVD) diamond disks in both transparent "white'' and opaque "black'' forms obtained from three different sources. The disks were nominally 0.635 cm in diameter and 254 μm thick. These strengths are explained by a theoretical model using a Young's modulus of 1.05×106 MPa and a fracture surface energy of 5.3 J/m2, appropriate for natural diamond, and with critical crack lengths between 33 and 105 μm. The latter lengths can fit, either on or inside, the tapered columnar crystal grains that grow vertically in synthetic CVD diamond films. The model is consistent with the observed inverse dependence of measured tensile strength on film thickness and with tensile strengths between 180 and 5190 MPa reported by other workers for synthetic CVD diamond. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359752
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  • 2
    Electronic Resource
    Electronic Resource
    26.1% solar cell efficiency for Ge mechanically stacked under GaAs (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 3010-3015 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have processed a diffused Ge wafer into a Ge concentrator solar cell and mechanically stacked it under a GaAs cell fabricated by Varian. We measured this stack's efficiency to be 26.1% for terrestrial air mass 1.5 direct (AM1.5D) conditions at a 285× concentration ratio. We showed that this efficiency is limited by optical absorption in the Varian GaAs cell caused by high 2–4 (1018) cm−3 substrate doping. We used a 2×1017 cm−3 doped GaAs filter to estimate the stack efficiency as 27.4%, which would be achieved with the same Varian GaAs cell formed on a lower doped substrate. We project efficiencies assuming the best properties reported for a GaAs device. This gives a 29.6% efficiency for an improved, planar Ge cell and 31.6% efficiency for a proposed point contact geometry for the Ge cell. The corresponding space (AM0) efficiencies at a 159× concentration ratio range from the 23.4% value we measured on the stack up to 28.4% projected for the point contact Ge place under the best GaAs cell. We showed that Ge cells give higher efficiencies than Si when stacked under GaAs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339389
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  • 3
    Electronic Resource
    Electronic Resource
    Optics and calculated efficiencies of mechanically stacked two-junction solar cells (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 694-699 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mechanically stacked two-junction solar cells avoid the multijunction problems of interfering growth conditions, shorting layers, and current matching. They also allow the use of well-developed Si and GaAs junctions. Doping the top junction substrates at 2(1017) cm−3 reduces measured free-carrier absorption by up to a factor of 5 compared to doping at 8(1017) cm−3. Separately measured quantum-yield spectra, open-circuit voltages, and fill factors provide the basis to calculate stack efficiencies of 24%–28% for Si stacked under GaAsP and GaAs top junctions for a direct air mass 1.5 (AM1.5D) terrestrial sunlight spectra and a 400× light concentration. The GaAs is a preferred top junction because it has a direct gap, operates at near its theoretical limits, and minimizes transmission loss effects by contributing over 70% of the total stack output without compromising potential stack performance. The open-circuit voltages of GaAs and Si cells are measured to vary with light intensity as predicted by the standard model with a junction ideality factor equal to 1.0. This and other experimental junction data provide the basis to calculate 400×, AM1.5D stack efficiencies of 29% for GaAs stacked on Ge and 30% for GaAs stacked on GaSb. Device improvements are suggested to project GaAs/Ge stack efficiencies of 30% and GaAs/GaSb stack efficiencies of 34% for 400×, AM1.5D. The 400×, AM0 efficiencies for space are 0.88 to 0.91 times the corresponding, terrestrial AM1.5D values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339744
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  • 4
    Electronic Resource
    Electronic Resource
    A new sequentially etched quantum-yield technique for measuring surface recombination velocity and diffusion lengths of solar cells (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 5150-5158 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have developed a new technique to characterize the individual layers of high-efficiency solar cells. In general, the technique allows one to set lower bounds for diffusion lengths and upper and lower bounds for interface recombination velocity. This is sufficient to determine which parameter limits performance, and often the actual parameter values are also determined accurately. We obtain this information by fitting a theoretical model to quantum-yield spectra measured on a sample in its initial state, and after its window passivation and top active layers are sequentially etched away. With such data on two p on n GaAs solar cells with AlxGa1−xAs passivation, we determined minority-carrier hole diffusion lengths of 1.0±0.2 and 0.2±0.05 μ in the Te-doped n layers for first and second samples, respectively. We found lower limits for the minority-carrier electron diffusion lengths in the top p layers of 2.0 μ in the carbon-doped first sample and 4.0 μ in the Mg-doped second sample. We determined interface recombination velocities of 4.0±0.5 (105) cm/s at the carbon-doped p layer's interface with its Al0.45Ga0.55As passivation layer, and between 500 and 104 cm/s for the Mg-doped layer's interface with its Al0.9Ga0.1As passivation layer. After stripping the AlxGa1−xAs layer away, we measured surface recombination velocities of 8.0±2.0 (106) cm/s on the carbon-doped sample, and 1.0±0.2 (107) cm/s on the Mg-doped sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338289
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of GaAs wafers and epilayers with electron-beam-induced current, etching, and reflected light (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 4248-4254 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used a combination of electron-beam-induced current (EBIC), etching, and optical measurements to show dramatic differences between the minority-carrier transport properties and defect structures in GaAs wafers from two different vendors. We found that the EBIC defects correspond to the traditional ones found with molten KOH etching and optical inspection. However, the EBIC micrographs give a great deal of additional information. The EBIC patterns from the first vendor's wafer showed diagonal striations and point defects that made the EBIC go to zero and were interconnected by wormlike lines. The second vendor's wafers showed EBIC point defects that only suppressed the response by 20% and gettered the surrounding material so that it had higher EBIC response. However, this second vendor's wafer had about a 15% overall lower EBIC response and a much higher density of surface polish defects identified by reflected light. Etching data showed that EBIC defects are bulk material properties and that electrochemical etching with a KOH electrolyte allows the wormlike defects to be seen optically in a Nomarski equipped microscope. Examination of epilayers showed that the wafer defects did not propagate up into a 4-μm-thick layer grown by vacuum chemical epitaxy or a 1.5-μm-thick layer grown by molecular-beam epitaxy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339098
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  • 6
    Electronic Resource
    Electronic Resource
    GaAs films grown by vacuum chemical epitaxy using thermally precracked trimethyl-arsenic (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 299-301 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Trimethyl-arsenic (TMAs) is used as a source of arsenic for GaAs film growth. In the process used, vacuum chemical epitaxy, TMAs is thermally decomposed into arsenic upstream in a hot cracker furnace. The arsenic and stable hydrocarbons are then transported in vacuum without condensation to the epitaxial growth zone. The hole carrier concentration and carbon content in grown films are studied via Hall, electrochemical profile, and secondary ion mass spectroscopy as a function of cracker furnace design. It is shown that when the TMAs decomposition efficiency is poor, the carbon content can be as high as 1019/cm3 but for a more efficient cracker, the carbon content can be reduced into the 1016/cm3 range. Toxic injury hazards can be reduced substantially by substituting TMAs for the more widely used arsine in GaAs growth systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339145
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  • 7
    Electronic Resource
    Electronic Resource
    GaSb films grown by vacuum chemical epitaxy using triethyl antimony and triethyl gallium sources (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 2861-2865 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaSb films have been grown using triethyl-Ga and triethyl-Sb sources. In a hot-wall reaction chamber located within a high-vacuum chamber, multiple group-III alkyl molecular beams are directed into the reaction chamber onto wafers. The group-V molecules are injected from the perimeter of the reaction chamber and undergo molecular flow across the deposition zone. The utilization efficiency of the group-V source material is enchanced by the use of a thermal cracker located at the point of group-V gas injection and by the use of the hot-wall chamber. Both unintentionally doped p-type and Te doped n-type GaSb films are grown and characterized. GaSb p-n junction photodiodes are also reported with internal quantum yields as high as 85%. Unintentionally doped films were shown to have background carrier concentrations of 4×1016 cm3 by capacitance versus voltage measurement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337881
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  • 8
    Electronic Resource
    Electronic Resource
    Measurement of a long diffusion length in a GaAs film improved by metalorganic-chemical-vapor-deposition source purifications (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 3784-3789 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The vacuum metalorganic-chemical-vapor-deposition (Vacuum MOCVD) process was combined with two source purifications to grow p-GaAs epitaxial films of high quality. Theoretical modeling of quantum yield spectra measured on a specially configured n+-p sample determined the minority-carrier electron diffusion length to be 10 μm to within a factor of 2 in the p layer. The p doping was reduced to the 5×1017 cm−3 level to avoid suppression of the diffusion length by Auger recombination. Multiple vacuum sublimations of dicyclopentadienyl magnesium (CP2Mg), the source of Mg for p doping, reduced the contamination by air and by cyclopentadiene (CP) by an order of magnitude. A dry ice/acetone cold trap was operated at slightly below 180-Torr pressure to reduce the water vapor content of arsine, used as the As source, from the hundreds of ppm down level down to the 2 ppm range. The vacuum growth process reduced residual gas contamination. These techniques were combined to grow a p on n GaAs solar cell with an efficiency of 24% at air mass 1.5 (AM1.5).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335592
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  • 9
    Electronic Resource
    Electronic Resource
    High-efficiency GaAs0.7P0.3 solar cell on a transparent GaP wafer (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 2302-2304 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fabrication of a high performance GaAs0.7P0.3 solar cell on a transparent GaP substrate with an AM1.5 efficiency of 15.4% for a concentration ratio of 30× is reported for the first time. The measured transparency of the GaP substrate allows these cells to be mechanically stacked on silicon solar cells in a manner that should yield combined conversion efficiencies well over 25%. This mechanically stacked two-band-gap cell design is particularly attractive because it utilizes the already well-developed Si solar cell and because the materials foundation for the GaAs0.7P0.3 on GaP cell has been laid by work on light emitting diodes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.334329
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  • 10
    Electronic Resource
    Electronic Resource
    Surface chemistry of CuxS and CuxS/CdS determined from x-ray photoelectron spectroscopy (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 5056-5065 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray photoelectron spectroscopy spectra measured on copper sulfide (CuxS) films showed that a thin surface reaction product containing Cu in the +2 valence state was formed on CuxS films exposed to air for 46 h at 40 °C and 90% relative humidity. An entirely different CuxS surface reaction product layer was formed in dry air at 170 °C for 30 min and it contained sulfur in the +6 valence state. The copper (Cu) valence state in CuxS was not found to be +2 even when the x value was less than 1.9. When the argon sputter-cleaned surface of CuxS or CuxS/CdS films was exposed to room-temperature air for 10 min, cadmium (Cd) atoms appeared on the CuxS surface. X-ray powder diffraction patterns showed that CuO and CdS reacted at 500 °C in flowing nitrogen to form Cu2S and CdO. This cation exchange between CdS and copper oxide may explain the surface Cd on the CuxS films. The standard free energy of reaction between CuO and CdS is positive while that between Cu2O and CdS is negative. These results indicate a method for stabilizing CuxS/CdS solar cells against degradation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335283
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