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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},
}