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@PHDTHESIS{Hpkes:55223,
      author       = {Hüpkes, Jürgen},
      title        = {{U}ntersuchung des reaktiven {S}putterprozesses zur
                      {H}erstellung von aluminiumdotierten {Z}inkoxid-{S}chichten
                      für {S}ilizium-{D}ünnschichtsolarzellen},
      volume       = {52},
      school       = {RWTH Aachen},
      type         = {Dr. (Univ.)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-55223},
      isbn         = {3-89336-435-8},
      series       = {Schriften des Forschungszentrums Jülich. Reihe
                      Energietechnik / Energy Technology},
      pages        = {X, 170 S.},
      year         = {2006},
      note         = {Record converted from VDB: 12.11.2012; RWTH Aachen, Diss.,
                      2005},
      abstract     = {This thesis addresses the development of aluminum doped
                      zinc oxide (ZnO:Al) films by reactive sputter deposition.
                      The study focuses on the relation between deposition
                      conditions and the resulting electrical, optical and
                      structural film properties. The structure of the ZnO:Al
                      films strongly affects the surface morphology obtained after
                      wet chemical etching. The technological goal was the design
                      of ZnO:Al films with optimized surface texture and thus
                      light scattering properties for the application as front
                      contact in amorphous (a-Si:H) and microcrystalline (μc-
                      Si:H) based thin film solar cells. The comparatively low
                      absorption coefficient of silicon in the long wavelength
                      range of the sun spectrum necessitates additional mechanisms
                      to enhance light absorption within the silicon layers. This
                      can be realized by a combination of rough, light scattering
                      front contacts and highly-reflective rear contacts.
                      Initially smooth, sputter deposited ZnO:Al films can be
                      roughened by post-deposition wet-chemical etching. In the
                      ideal case, these rough layers introduce almost completely
                      diffuse transmission, and back reflector and front contact
                      guide the light through the silicon layers until it is
                      totally absorbed (ideal light trapping). The ZnO:Al films
                      were prepared by reactive mid-frequency (MF) sputtering from
                      metallic Zn:Al targets in a vertical in-line deposition
                      system. Initially, technological aspects like stabilization
                      of the working point and the influence of substrate movement
                      required for dynamic deposition were studied. Doping
                      concentration and deposition conditions were varied to
                      optimize the optical and electrical ZnO:Al properties,
                      leading to resistivities ρ < 3 · 10$^{−4}$ Ωcm and at
                      the same time transmission values exceeding 80 \% in the
                      visible and near infrared spectrum. By increasing deposition
                      pressure, decreasing substrate temperature or shifting the
                      working point towards the oxide mode, the surface morphology
                      after etching in diluted hydrochloric acid could be changed
                      from crater-like to granular shapes. The working point
                      during reactive sputtering enables the density of points of
                      etch attack in post-deposition etching steps to be varied
                      over a wide range. In subsequent discussion concerning the
                      etching behavior of sputter deposited ZnO:Al films in acids
                      and bases, known dependencies are identified and some
                      analogies to the etching of ZnO single crystals are drawn.
                      Based on the experimental findings we developed an optimized
                      high rate deposition process including post-deposition
                      etching for surface textured ZnO:Al films. When applied as a
                      front contact in solar cells, initial efficiencies of 9.9 \%
                      and 8.2 \% were realized for single junction cells with
                      a-Si:H and μc-Si:H absorber layers, respectively. These
                      ZnO:Al front contacts were sputtered at dynamic deposition
                      rates of 100 nm·m/min which correspond to static deposition
                      rates as high as 400 nm/min. For an a-Si:H/μc-Si:H tandem
                      structure solar module, an initial aperture area efficiency
                      of 9.7 \% was obtained on 64 cm$^{2}$ aperture area.},
      cin          = {IPV},
      ddc          = {620},
      cid          = {I:(DE-Juel1)VDB46},
      pnm          = {Erneuerbare Energien},
      pid          = {G:(DE-Juel1)FUEK401},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/55223},
}