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@PHDTHESIS{Sommer:818286,
      author       = {Sommer, Nicolas},
      title        = {{C}onductivity and {S}tructure of {S}puttered {Z}n{O}:{A}l
                      on {F}lat and {T}extured {S}ubstrates for {T}hin-{F}ilm
                      {S}olar {C}ells},
      volume       = {328},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2016-04760},
      isbn         = {978-3-95806-156-9},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {vii, 195, XIV S.},
      year         = {2016},
      note         = {RWTH Aachen, Diss., 2016},
      abstract     = {Aluminum-doped zinc oxide (ZnO:Al) is a prominent
                      representative of the material class denoted as transparent
                      conductive oxides (TCO). TCOs feature electrical
                      conductivity while being transparent in the visible range.
                      These unique properties constitute the wide application of
                      TCOs in opto-electronic devices. This work targets the
                      application of TCOs for thin-film silicon and
                      chalcopyrite-based solar cells. Generally, TCOs are
                      deposited onto at substrates. However, TCO growth on
                      textured, light scattering substrates for thin-film silicon
                      solar cells and on the rough chalcopyrite absorber also call
                      for the optimization of TCO deposition on textured
                      substrates. Therefore, the deposition of sputtered ZnO:Al on
                      at as well as on textured substrates is elaborated. The
                      focus is the understanding and optimization of electrical
                      conductivity accompanied by a detailed investigation of the
                      material's structural properties. On at substrates, I
                      propose a conductivity model that comprises three scattering
                      mechanisms, namely ionized-impurity, electron-phonon, and
                      grain boundary scattering. The prominent feature of the
                      model is the analytical description of grain boundary
                      scattering by feld emission, i.e. quantum mechanical
                      tunneling of electrons through potential barriers at grain
                      boundaries. For this purpose, a theory of Stratton(R.
                      Stratton, $\textit{Theory of Field Emission from
                      Semiconductors}$, Phys. Rev. $\textbf{125}$ (1962), 67 - 82)
                      is adapted to double Schottky barriers at grain boundaries.
                      The conductivity model is applied to a wide range of
                      literature data to show its applicability and explanatory
                      power. After establishing the basic understanding of ZnO:Al
                      conductivity, two optimization routes are presented. The
                      first route allows for a reduction of deposition temperature
                      by 100 $^{\circ}$C without deteriorating conductivity,
                      transparency, and etching morphology by means of a seed
                      layer concept. Seed and subsequently grown bulk layers were
                      deposited from ZnO:Al$_{2}$O$_{3}$ targets with 2 wt\% and 1
                      wt\% Al$_{2}$O$_{3}$, respectively. I investigated the
                      effect of bulk and seed layer deposition temperature as well
                      as seed layer thickness on electrical, optical, and
                      structural properties of ZnO:Al films. The positive effect
                      of the highly doped seed layer was attributed to the
                      beneficial role of the dopant aluminum that induces a
                      surfactant effect. Furthermore, the seed layer induced
                      increase of tensile stress is explained on the basis of the
                      grain boundary relaxation model. Finally,
                      temperature-dependent conductivity measurements, optical
                      fits, and etching characteristics revealed that seed [...]},
      cin          = {IEK-5},
      cid          = {I:(DE-Juel1)IEK-5-20101013},
      pnm          = {121 - Solar cells of the next generation (POF3-121)},
      pid          = {G:(DE-HGF)POF3-121},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:0001-2016092811},
      url          = {https://juser.fz-juelich.de/record/818286},
}