Publications Search Results

Now showing 1 - 10 of 14
  • Publication
    One-step transfer printing of patterned nanogap electrodes
    ( 2019)
    Saller, K.B.
    ;
    Riedl, H.
    ;
    Lugli, P.
    ;
    Koblmüller, G.
    ;
    Tornow, M.
    Direct printing of nanogap-separated metallic contact pairs is described that enables novel nanoelectronic device architectures. Nanotransfer printing (nTP) stamps are grown by molecular beam epitaxy involving layered III-V semiconductors that are selectively etched. Finished stamps comprise both the nanoscale surface trench that becomes the nanogap on printing and a microscale, predetermined geometry that affords the simultaneous integration of contact pads for external electrical testing. This nTP technique is well suited for top-contacting sensitive thin films for electrical characterization; a typical electrode configuration is illustrated by transfer-printed 13 nm thin metal films that are separated by an electrically insulating gap of ca. 30 nm.
  • Publication
    Subcell characterization in multijunction solar cells using pulsed light
    ( 2017)
    Rutzinger, M.
    ;
    Salzberger, M.
    ;
    Nesswetter, H.
    ;
    Lackner, D.
    ;
    Bett, A.W.
    ;
    Lugli, P.
    ;
    Zimmermann, C.G.
    The photocurrent versus open-circuit voltage characteristic of individual subcells in a multijunction solar cell can be measured by illuminating the subcell with a pulse sequence of spatially homogeneous laser light. In this paper, we demonstrate the applicability of this method for four junction solar cells. Furthermore, the degradation of triple junction solar cells after electron irradiation is analyzed on the subcell level. Subcell performance parameters are derived, and results are compared with electroluminescence-based results. The influence of luminescent coupling and semitransparency effects to lower subcells are quantified by stimulations.
  • Publication
    Determination of subcell I-V characteristics of multijunction solar cells using optical coupling
    ( 2016)
    Nesswetter, H.
    ;
    Jost, N.R.
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    Lugli, P.
    ;
    Bett, A.W.
    ;
    Zimmermann, C.G.
    A method for the determination of the subcell I-V characteristics of multijunction solar cells in the presence of optical coupling is presented and applied to a Ga0.50In0.50P/Ga0.99In0.01As/Ge triple-junction solar cell. Each of the subcells is described by a two-diode model and can be illuminated by a narrowband light source externally. Optical coupling is then used explicitly to generate current in one subcell, which is not illuminated externally. This approach yields the magnitude of optical coupling and a relationship between the two diode parameters of each subcell. The remaining cell parameters are determined with the help of pulsed illumination. In this fashion, the open circuit voltage of individual subcells is accessible, despite the fact that not all junctions are illuminated.
  • Publication
    Determination of subcell open circuit voltages and Iph-Voc curves in multijunction solar cells by sequentially pulsed, monochromatic illumination
    ( 2016)
    Rutzinger, M.
    ;
    Nesswetter, H.
    ;
    Lugli, P.
    ;
    Bett, A.W.
    ;
    Zimmermann, C.G.
    The open circuit voltages Voc of individual subcells in a multijunction solar cell are measured by illuminating a given subcell with a pulse of spatially homogeneous, nearly monochromatic light with a rising edge in the ms regime. The influence of luminescent coupling and semi-transparency on Voc is eliminated by over-illuminating all subcells below this subcell with a preceding light pulse. By using a suns-Voc approach, the two-diode model dark saturation currents of each subcell are extracted. The proposed method is verified experimentally as well as through simulations on three and four-junction solar cells.
  • Publication
    Determination of subcell I-V parameters by a pulsed suns-Voc method including optical coupling
    ( 2015)
    Nesswetter, H.
    ;
    Jost, N.R.
    ;
    Lugli, P.
    ;
    Bett, A.W.
    ;
    Zimmermann, C.G.
    The open circuit voltage of a single subcell in a multijunction cell stack can be measured with the help of pulsed, millisecond illumination. This concept makes use of the fact that the charging of the non-illuminated cell capacitances takes place on a much longer timescale than of the illuminated one. Optical coupling introduces a photocurrent in the subcell underneath. Its efficiency can be quantified in parallel under short circuit conditions. A suns-Voc approach, applied to this subcell pair, yields all relevant diode parameters. Applied to all subcells of a Ga0.50In0.50P/Ga0.99In0.01As/Ge triple junction cell, a very good match to the dark I-V curve is obtained.
  • Publication
    Physical unclonable functions based on crossbar arrays for cryptographic applications
    ( 2013)
    Lugli, P.
    ;
    Mahmoud, A.
    ;
    Csaba, G.
    ;
    Algasinger, M.
    ;
    Stutzmann, M.
    ;
    Rührmair, U.
    Due to their attractive, regular structure and their simple implementation, crossbar arrays have become one major emerging research area in the fields of nano-devices and electronic circuits. This paper discusses novel applications of crossbars as various types of so-called physical unclonable functions (PUFs) in the field of physical cryptography. The latter is a recent branch of cryptography and security that exploits the inherent, small-scale randomness and disorder in physical structures. PUFs are the currently dominant primitive within this new field. In order to establish the applicability of crossbar structures as PUFs, two crossbars with rectifying junctions are investigated on the basis of real measurement data. In addition, the scalability of these crossbars with respect to their power dissipation and noise margin is evaluated in simulations. The types of PUFs as which crossbars can serve include weak PUFs and super high information content PUFs. We also discu ss whether crossbar-based PUFs allow the erasure and/or rewriting of response information on a single challenge-response-pair level, i.e. without affecting other PUF responses.
  • Publication
    Electroluminescence and photoluminescence characterization of multijunction solar cells
    ( 2013)
    Nesswetter, H.
    ;
    Lugli, P.
    ;
    Bett, A.W.
    ;
    Zimmermann, C.G.
    A combined electroluminescence and photoluminescence setup for a fast, nondestructive, and high-resolution characterization of large-area lattice matched GaInP2 /Ga(In)As/Ge triple-junction space solar cells was developed. In contrast with electroluminescence, where coupling effects between the subcells appear, all subcells can be analyzed independently in photoluminescence imaging, using three monochromatic light sources. This will be demonstrated by way of example for a partly irradiated cell. Alternatively, electroluminescence combined with simulation program with integrated circuit emphasis network simulations constitutes a powerful tool to extract quantitative information despite the coupling effects. Sheet resistances and shunts in individual subcells can be accurately modeled with this method.
  • Publication
    Luminescence based series resistance mapping of III-V multijunction solar cells
    ( 2013)
    Nesswetter, H.
    ;
    Dyck, W.
    ;
    Lugli, P.
    ;
    Bett, A.W.
    ;
    Zimmermann, C.G.
    A method to measure the series resistance of Ga0.5In0.5P/Ga(In)As/Ge triple-junction solar cells spatially resolved is developed, based on luminescence imaging. With the help of network simulations, the dependence of the local series resistance on the external subcell illumination intensities and biasing voltage is predicted and the optimum measurement conditions are clarified. Experimentally, specially prepared test cells with partially irradiated areas are used to verify the capabilities of the method. It is shown that the method is not sensitive to variations of the dark I-V parameters of the subcells.
  • Publication
    Series resistance mapping of III-V multijunction solar cells based on luminescence imaging
    ( 2013)
    Nesswetter, H.
    ;
    Dyck, W.
    ;
    Lugli, P.
    ;
    Bett, A.W.
    ;
    Zimmermann, C.G.
    A method for spatially resolved series resistance measurements of Ga0.5In0.5P/Ga(In)As/Ge triple-junction solar cells based on electro- and photoluminescence imaging is presented. The results gained from luminescence images of all three subcells clearly indicate the main contributions to the series resistance like interrupted gridfingers, the frontside metallization itself and the top cell emitter layer. Test cells with partially electron irradiated areas are used to demonstrate that the method is not sensitive to inhomogeneous dark I-V parameters.
  • Publication
    Electroluminescence and photoluminescence characterization of multijunction solar cells
    ( 2012)
    Nesswetter, H.
    ;
    Lugli, P.
    ;
    Bett, A.W.
    ;
    Zimmermann, C.G.
    A combined electroluminescence and photoluminescence setup for a fast, nondestructive, and high-resolution characterization of large-area lattice matched GaInP2 /Ga(In)As/Ge triple-junction space solar cells was developed. In contrast with electroluminescence, where coupling effects between the subcells appear, all subcells can be analyzed independently in photoluminescence imaging, using three monochromatic light sources. This will be demonstrated by way of example for a partly irradiated cell. Alternatively, electroluminescence combined with simulation program with integrated circuit emphasis network simulations constitutes a powerful tool to extract quantitative information despite the coupling effects. Sheet resistances and shunts in individual subcells can be accurately modeled with this method.