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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4586-4590 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A frequently used front contact in CdS/CdTe heterojunction solar cells is SnO2. We have performed a soft x-ray synchrotron radiation photoemission investigation of the formation and thermal stability of the SnO2/CdS interface in an attempt to understand how device processing influences this interface. The most important results are that (1) the CdS and SnO2 do not interact chemically, even after annealing to 400 °C, (3) the first ∼16 A(ring) CdS deposited on polycrystalline SnO2 grows in a layer-by-layer mode, (3) subsequent CdS layers agglomerate, forming a topologically rough surface, (4) diffusion of Sn, Cd, and S across the interface does not occur, (5) annealing a CdS thin film grown at room temperature on SnO2 to 400 °C enhances the agglomeration, and (6) the near coincidence of the conduction-band minimum across the interface facilitates ohmic contact between n-type CdS and n-type SnO2.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5888-5891 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Synchrotron radiation soft x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the CdS(In)/CuInSe2 heterojunction interface. In-doped CdS overlayers were deposited in steps on single-crystal n-type CuInSe2 at 250 °C. Results indicate that the CdS(In) grows in registry with the substrate, initially in a two-dimensional growth mode followed by three-dimensional island growth as is corroborated by reflection high-energy electron diffraction analysis. Photoemission measurements were acquired after each growth in order to observe changes in the valence-band electronic structure. The results were used to correlate the interface chemistry with the electronic structure at these interfaces and to directly determine the CdS(In)/CuInSe2 heterojunction valence-band discontinuity and the consequent heterojunction band diagram as a function of In dopant concentration. We measured a valence-band offset ΔEv=0.3 eV, independent of In doping.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 8381-8385 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We studied the structural and electronic properties of the ZnTe/CdTe(100) interface with reflection high-energy electron diffraction and angle-resolved synchrotron radiation photoemission spectroscopy (ARPES). ZnTe overlayers grown at 300 °C on CdTe(100) were fully strained and pseudomorphic up to ≈16 A(ring). Beyond this coverage the ZnTe film starts to gradually relax the 6.6% in-plane lattice strain. Complete relaxation is reached at a ZnTe coverage of ∼300 A(ring). A valence-band offset of ΔEv=0.00±0.05 eV was measured with ARPES at the Γ point. This propitious band lineup may allow for the use of a ZnTe intermediate layer at metal/CdTe structures to induce ohmic back contacts in CdS/CdTe heterojunction solar cells.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Strain relaxation at the lattice mismatched CdS/GaAs (100) interface has been investigated by reflection high-energy electron diffraction (RHEED) and Raman scattering. In-situ RHEED measurements indicate a gradual relief of the mismatch strain once the critical film thickness is exceeded. After-growth Raman measurements reveal that the strain profile measured by RHEED remains "frozen'' in the grown layer except very close to the CdS/GaAs interface, where further relaxation takes place. A microscopic calculation shows that the presence of nonuniform strain leads to phonon confinement effects, as localized modes appear in regions of similar strains.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1617-1617 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: During the last few years considerable effort was spent at various laboratories to evaluate the possibilities of optical devices to generate circularly polarized synchrotron radiation. These instruments convert linearly polarized radiation by utilizing the phase-shifting properties of multiple reflectors or multilayer transmission optics. In the VUV and soft-x-ray range, the figure of merit TP2, where P is the degree of circular polarization and T the optical transmission, of specially tailored reflection coatings or multilayer structures can be considerably higher than what can be achieved with conventional insertion devices such as the crossed field undulator. In addition to being considerably less expensive, the various optical designs have the great advantage of not being an integral part of the storage ring and, as such, completely transparent to the operation and other users of the storage ring. Various phase-shifter designs will be discussed in terms of their performance, e.g., optical throughput, degree of polarization, and capabilities to modulate between left and right circular light. Recent MCD experiments utilizing optical phase shifters not only demonstrate the proof of principle, but also provide strong evidence of the potential capabilities of "optical insertion'' devices as an alternative tool to generate variably polarized synchrotron radiation. © 1995 American Institute of Physics.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We discuss the complexities of controlling the new high-resolution soft x-ray beamline at the University of Wisconsin Synchrotron Radiation Center. A monochromator at the heart of the beamline utilizes a combined rotation and translation of a variable line spaced grating to minimize major aberration terms. A rotational accuracy of 0.12 arcsec and a translational accuracy of 10 μm are required for the combined motions to obtain the desired resolution. A rotational resolution of better than 0.01 arcsec was achieved with the use of a laser interferometer and piezoelectric actuator for submicrometer feedback control. The translation control uses a linear encoder with a resolution of 0.1 μm and a motorized feedback loop. A calculation overhead of less than 100 μs for each movement was obtained by using a spline fit to approximate the rotational and translation positions to the required accuracy. © 1995 American Institute of Physics.
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We built a quadruple reflection polarizer which can be used in the energy range hν=8–130 eV to convert linearly polarized synchrotron radiation into circularly polarized light of either left or right handedness. The design permits independent adjustment of the angle of reflection θ as well as the angle of rotation α along the light axis. These adjustments allow us to operate the polarizer at any given energy in a mode where either the degree of circular polarization Pcirc or the figure of merit TP2circ is maximized. We tested the optical performance and phase shifting properties of a prototype polarizer using a bending magnet beamline. The data verify our model calculations of the conversion efficiency and the optimum operating parameters to maintain the highest degree of circular polarization. © 1995 American Institute of Physics.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the first magnetic circular dichroism (MCD) measurements around the M edges of 3d metals utilizing SRCs recently developed quadruple reflection polarizer system. The reflection polarizer converts linearly polarized light by means of the phase shift between s- and p-reflections into either left or right circular polarized radiation. The concept of the phase shifter has been tested at a bending magnet beam line at the Aladdin storage ring using the M2,3 absorptions of magnetically ordered thin films of Fe, Co and Ni. The normalized MCD signal e.g., (IR−IL)/0.5*(IR+IL) is on the order of several % from peak to peak and scales linearly with the magnetic moments. The shape of the reflection MCD signals has a very pronounced angular dependence with a maximum around a reflection angle of θ=60°–65°. The main trends in the angular dependence of the reflection MCD signal can be verified by model calculations. The model also allows us to extract the energy dependence of the off-diagonal terms in the dielectric tensor from the experimental data. The potential use and high sensitivity to variations in the local magnetic environment will be demonstrated with high resolution measurements of several ferrimagnetic compounds. © 1996 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4489-4493 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two experiments designed to assist in understanding the physics of certain back contacts on p-type CdTe solar-cell devices are described. In the first experiment, x-ray photoelectron and Auger electron spectroscopies are used to show that etching CdTe in HNO3:H3PO4 results in a Te layer on the CdTe surface. In the second experiment, photoemission spectroscopy is used to explore the electronic properties of evaporated Te deposited on thin-film, polycrystalline p-CdTe in an effort to develop a band diagram for the Te/p-CdTe interface. The motivation for developing the band diagram derives from previous observations that chemically etching polycrystalline p-CdTe solar-cell device material before application of the back contact reduces the series resistance of the device. The key results are that the evaporated Te overlayer is p type and that the valence-band offset between Te and p-CdTe is favorable for low-series-resistance contact, ΔEv=0.26±0.1 eV. © 1995 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 2858-2860 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A formalism is developed to interpret the magnetic circular dichroism (MCD) sum rules in terms of the complex dielectric tensor ε(ω). Utilizing classical Maxwell–Fresnel theory, the formalism is applied to the reflection spectra of Fe at the M2,3 transition to calculate the orbital moments 〈Lz〉. The analysis shows that due to the energy dependence of the unpolarized normalization integral and the absence of a well-defined cut-off energy across the transition edge, large errors can be introduced. Uncertainties in 〈Lz〉 by more than 100% are possible which makes a comparison with other literature values questionable. Due to the arbitrary energy cut-off, the application of the sum rules as a general tool to unambiguously decompose MCD spectra into orbital and spin components should be practiced with great caution. © 1998 American Institute of Physics.
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