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  • 1
    Electronic Resource
    Electronic Resource
    Dynamics of current filaments in p-type germanium under the influence of a transverse magnetic field (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 232-235 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An explanation for the self-generated formation of spontaneous current oscillations developing during low-temperature impact ionization breakdown of slightly doped p-type germanium is presented for the first time, taking advantage of a model experiment. Upon applying a relatively small transverse magnetic field, the spatially inhomogeneous current distribution manifest in the form of individual high-conducting-current filaments undergoes a distinct traveling dynamics that is oriented perpendicular to the direction of the electric and the magnetic field (i.e., not coincident with the direction of the current flow). The resulting magnetic-field-induced oscillatory behavior can be described qualitatively by simple model considerations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350316
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic properties of CuGaSe2-based heterojunction solar cells. Part I. Transport analysis (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 584-593 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article presents a systematic study on the electronic transport mechanisms of CuGaSe2-based thin film solar cells. A variety of samples with different types of stoichiometry deviations, substrates and buffer layers is investigated. We propose two transport models, namely tunneling enhanced volume recombination and tunneling enhanced interface recombination, which allow to explain the observed features for all devices under consideration. The doping level of the absorber layer turns out to be the most decisive parameter for the electronic loss mechanism. The doping is influenced by the type of stoichiometry deviation as well as by the Na content of the substrate. High doping levels result in tunnel assisted recombination. The best solar cells display the lowest tunneling rates. For these devices treatments of the absorber surface by air-annealing and/or the deposition temperature of the CdS buffer layer are decisive for the final device performance. We use the investigation of the open-circuit voltage relaxation to verify the assumptions on the dominant loss mechanism in the different devices. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371903
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  • 3
    Electronic Resource
    Electronic Resource
    Defect generation in Cu(In,Ga)Se2 heterojunction solar cells by high-energy electron and proton irradiation (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 650-658 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate irradiation-induced defects in high-efficiency Cu(In,Ga)Se2/CdS/ZnO heterojunction solar cells after electron irradiation with energies of 0.5, 1, and 3 MeV and after 4 MeV proton irradiation. We use electron and proton fluences of more than 1018 cm−2 and up to 1014 cm−2, respectively. The reduction of the solar cell efficiency in all experiments is predominantly caused by a loss ΔVOC of the open circuit voltage VOC. An analytical model describes ΔVOC in terms of radiation-induced defects enhancing recombination in the Cu(In,Ga)Se2 absorber material. From our model, we extract defect introduction rates for recombination centers in Cu(In,Ga)Se2 for the respective particles and energies. We directly monitor the defect generation of these radiation-induced defects by admittance spectroscopy. The decrease of effective doping density in the Cu(In,Ga)Se2 absorber layer under particle irradiation is analyzed with capacitance voltage measurements at low temperatures. Furthermore, data on the relative damage coefficients for high-energy electron irradiation in Cu(In,Ga)Se2 solar cells are presented. All data, from electron as well as proton irradiations, merge to a single characteristic degradation curve. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1379348
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  • 4
    Electronic Resource
    Electronic Resource
    Oxygenation and air-annealing effects on the electronic properties of Cu(In,Ga)Se2 films and devices (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 497-505 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Post-deposition air-annealing effects of Cu(In,Ga)Se2 based thin films and heterojunction solar cell devices are studied by photoelectron spectroscopy and admittance spectroscopy. Ultraviolet photoelectron spectroscopy reveals type inversion at the surface of the as-prepared films, which is eliminated after exposure of several minutes to air due to the passivation of surface Se deficiencies. X-ray photoelectron spectroscopy demonstrates that air annealing at 200 °C leads to a decreased Cu concentration at the film surface. Admittance spectroscopy of complete ZnO/CdS/Cu(In,Ga)Se2 heterojunction solar cells shows that the Cu(In,Ga)Se2 surface type inversion is restored by the chemical bath used for CdS deposition. Air annealing of the finished devices at 200 °C reduces the type inversion again due to defect passivation. Our results also show that oxygenation leads to a charge redistribution and to a significant compensation of the effective acceptor density in the bulk of the absorber. This is consistent with the release of Cu from the absorber surface and its redistribution in the bulk.© 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370758
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  • 5
    Electronic Resource
    Electronic Resource
    Recombination mechanisms in amorphous silicon/crystalline silicon heterojunction solar cells (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2639-2645 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article investigates limitations to the open circuit voltage of n-type amorphous silicon/p-type crystalline silicon heterojunction solar cells. The analysis of quantum efficiency and temperature dependent current/voltage characteristics identifies the dominant recombination mechanism. Depending on the electronic quality of the crystalline silicon absorber, either recombination in the neutral bulk or recombination in the space charge region prevails; recombination at the heterointerface is not relevant. Although interface recombination does not limit the open circuit voltage, recombination of photogenerated charge carriers at the heterointerface or in the amorphous silicon emitter diminishes the short circuit current of the solar cells. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372230
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  • 6
    Electronic Resource
    Electronic Resource
    Composition dependence of defect energies and band alignments in the Cu(In1−xGax)(Se1−ySy)2 alloy system (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1391-1399 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The composition dependence of defect energies in polycrystalline Cu(In1−xGax)(Se1−ySy)2 chalcopyrite thin films is investigated by admittance spectroscopy of ZnO/CdS/chalcopyrite heterojunctions. We determine the band alignments within the polycrystalline Cu(In1−xGax)(Se1−ySy)2 semiconductor system using the energy position of the dominant acceptor state as a reference level. Upon alloying CuInSe2 with S the activation energy of the acceptor increases from 300 meV to approximately 380 meV in CuIn(Se0.4S0.6)2. A similar result holds when using Cu(In1−xGax)(Se1−ySy)2 with x(approximate)0.3. In contrast, the acceptor activation energy remains essentially unchanged in the Cu(In1−xGax)Se2 alloy system over the whole composition range 0≤x≤1. Taking the acceptor energy as reference, we find a valence band offset ΔEV=−0.23 eV between CuInSe2 and CuInS2. The same valence band offset is found between Cu(In0.7Ga0.3)Se2 and Cu(In0.7Ga0.3)S2. In contrast, the combination CuInSe2/CuGaSe2 displays ΔEV below 0.04 eV. Our results indicate that a bulk reference level exists in the Cu(In1−xGax)(Se1−ySy)2 semiconductors which sets the band structure on a common energy scale, thus establishing the natural band lineups within the alloy system automatically. This conclusion is sustained by our finding that the position of the Fermi level at the CdS/chalcopyrite interface exhibits a constant energy distance to the acceptor level. The concentration of bulk acceptors is in addition correlated to the open circuit voltage losses of heterojunction solar cells. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1432126
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  • 7
    Electronic Resource
    Electronic Resource
    Electronic properties of CuGaSe2-based heterojunction solar cells. Part II. Defect spectroscopy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 594-602 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CuGaSe2/CdS/ZnO heterostructures with different CuGaSe2 stoichiometry deviations, glass substrates with different Na content and varying CdS buffer deposition procedures are analyzed with admittance spectroscopy, deep level transient spectroscopy, and capacitance–voltage measurements. Cu-rich CuGaSe2 exhibits two acceptor-like bulk traps with activation energies of 240 and 375 meV. The density of both defect states is reduced by air annealing at 200 °C. Ga-rich CuGaSe2 material displays a tail-like energetic distribution of acceptor defects. The maximum of this distribution is at an energy of 250 meV. Defect densities and doping concentrations of Ga-rich material are considerably lower than in Cu-rich material. The different defect and doping densities found in the present investigation fully explain the efficiency gain which has recently been made by changing the material stoichiometry, the glass substrate and the CdS-deposition method for CuGaSe2-based thin film solar cells. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371904
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  • 8
    Electronic Resource
    Electronic Resource
    Band offset variations at Ge/GaAs (100) interfaces (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 261-263 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We analyze the band offsets at Ge/GaAs (100) interfaces by internal photoemission, capacitance/voltage and current/voltage measurements. The conduction band offset varies with Ge growth temperature from −0.025 eV for 300 °C to 0.33 eV for 500 °C. We attribute these drastic offset variations to different microscopic interface configurations at the polar Ge/GaAs (100) heterojunction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108983
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  • 9
    Electronic Resource
    Electronic Resource
    Tunneling-enhanced recombination in Cu(In, Ga)Se2 heterojunction solar cells (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 111-113 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This letter presents an analytical model for tunneling-enhanced recombination current in the space charge region of semiconductor junctions. We investigate current–voltage characteristics of different types of Cu(In, Ga)Se2-based heterojunction solar cells in a temperature range from 100 to 340 K. The temperature dependence of the saturation current and of the diode ideality factor of these devices are well described by the closed form expressions derived by the present approach. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122967
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  • 10
    Electronic Resource
    Electronic Resource
    Persistent photoconductivity in Cu(In,Ga)Se2 heterojunctions and thin films prepared by sequential deposition (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 223-225 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A characteristic, reversible metastability is observed for Cu(In,Ga)Se2 thin films and ZnO/CdS/Cu(In,Ga)Se2 heterojunctions. Annealing at 80 °C leads to a decrease of the dark conductivity of the thin films by up to a factor of 2 at room temperature and several orders of magnitude when measured at lower temperatures. By exposure to light, the initial state can be re-established. This reenhancement of the dark conductivity can be looked at as persistent photoconductivity. Admittance measurements at Cu(In,Ga)Se2 heterojunction solar cells display a reversible shift of the activation energy of a distinct dielectric loss peak ranging from 70 to about 160 meV upon illumination or annealing at 80 °C, respectively. We propose that both phenomena as well as commonly observed light-soaking effects of Cu(In,Ga)Se2 solar cells have a common origin. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121762
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