ICMCTF 2012! - CD-Lab Application Oriented Coating Development

[1] T. Yamada et al., Appl. Phys. Lett. 91, 051915 (2007); J. Appl. Phys.
107, 123534 (2010).
[2] T. Shibata et al., Adv. Mater. 20, 231 (2008).
10:00am C4-1-7 Optical and Electrical Characterization of Ga-doped
ZnO Thin Films Grown by Atmospheric Spray Pyrolysis, K. Yoshino
(t0b114u@cc.miyazaki-u.ac.jp), N. Kamiya, M. Oshima, University of
Miyazaki, Japan
ZnO attaracts attention as a substitute of indium tin oxide because ZnO is a
low cost and abundant. material. ZnO has shown promise for many
applications including gas sensors, transport electrodes, piezoelectric
devices, varistors and surface acoustic wave devices. Its direct optical
bandgap of 3.4 eV at room temperature is wide enough to transmit most of
the useful solar radiation in ZnO/CuInSe2 based solar cells. Furthermore,
ZnO is a good candidate to substitute for ITO (In-doped In2O3) and FTO (Fdoped
SnO2) in transparent conductive electrodes. Many techniques have
been employed to produce the ZnO thin films including molecular beam
epitaxy, metal organic chemical vapor deposition, radio frequency
magnetron sputtering, spray pyrolysis and sol-gel methods. Furthermore,
low temperature growth of ZnO is important for compatibility with
photovoltaic device fabrication processes. In our previous work [1],
undoped ZnO films on glass substrates were grown by a spray pyrolysis
method at room temperature (RT, ~ 300 ˚C). Polycrystalline ZnO thin films
were successfully grown at RT under an air atmosphere. Diethylzinc (DEZ)
was used as the Zn source material. The DEZ solution was diluted by some
solvent in order to use safely under an air atmosphere. X-ray diffraction
indicates that (10-10) and (10-11) peaks are dominant. The lattice constants
of the a and c axes are larger than that of ICDD data. The samples develop a
c axis (0002) orientation with increasing substrate temperature.
Furthermore, the lattice constants of the a and c axes become closer to those
of ICDD data with increasing substrate temperatures. In this work, growth
of Ga-doped ZnO/PET film using DEZ solution was carried out by spray
pyrolysis at 150°C . The average transmittance of undoped and Ga-doped
ZnO films showed 80%. The sheet resistivity of Ga-doped ZnO decreased
to 50 W/sq. by UV irradiation for 120min.[1] K. Yoshino, Y. Takemoto, M.
Oshima, K. Toyota, K. Inaba, K. Haga, K. Tokudome, Jpn. J. Appl. Phys.
50 (2011) 040207.
10:20am C4-1-8 Investigation of different techniques for achieving
optimal p-type doping in transparent conductive zinc oxide by a metalnitride
codoping approach, A. Poppleton
(alice.poppleton@sydney.edu.au), M. Bilek, D. McKenzie, University of
Sydney, Australia, S. Lim, Lawrence Berkeley National Laboratory, US, B.
Abendroth, TU Bergakademie Freiberg, Germany
Transparent conducting oxides (TCOs) are a crucial component of many
modern technologies. The demand for transparent conductors is high and
rapidly growing. The most common TCO used in these technologies is ITO.
Unfortunately indium is rare, expensive, toxic and particularly difficult and
environmentally damaging to extract. Additionally, TCOs based on the
indium-tin system are unavoidably n-type, limiting their usefulness to only
transparent metal-imitators.
An extremely promising alternative TCO is ZnO. It is preferable to ITO in
several regards. Zinc is a cheap, abundant, environmentally and biologically
benign element, making processing and disposal much simpler and safer.
Unlike ITO, ZnO can theoretically be both n- and p-type doped, leading to
potential applications in transparent electronics, novel solar cells, and,
owing to its ~2.4 eV bandgap, UV LEDs and laser diodes.
In this paper we investigate a range of techniques for deposition of intrinsic
ZnO, in order to find an optimal technique for production of a highly
transparent, low defect, high resistivity material as a foundation for a
higher-quality doped material. We compare magnetron sputtering with
cathodic arc plasma deposition, and HiPIMS, a novel deposition technique
which gives a highly ionised plasma in a magnetron sputtering system.
We also investigate codoping as a way to achieve p-type doping. Due to its
similar size to oxygen, low toxicity, and abundance, N is a popular
candidate for p-type doping in ZnO. It is widely recognised that doping with
N alone is ineffective, due to poor solubility of the dopant and depth of the
acceptor level within the band. To overcome both of these problems, a
metal-nitride codoping approach has been suggested, improve nitrogen
solubility and build up the valence band edge, solving the acceptor depth
problem. Recently, Duan et al. (PRB 83, 2011) have performed firstprinciples
DFT calculations which indicate that TiN may surpass the
popular AlN and GaN as a codoping material, due to the exeptional stability
of the TiN4 complex in ZnO. It may also be more efficient, as each TiN4
cluster should act as a double acceptor.
To date, achieving an excess of available nitrogen relative to metal dopant
has been a significant experimental stumbling block for all codoping
approaches. We examine methods to enhance available nitrogen in the
deposition plasma. In particular, we report on the degree of N incorporation
Tuesday Morning, April 24, 2012 32
from regular DC magnetron sputtering plasma, compared with injection of
gas at the target in HiPIMS and DC arc depositions, as well as the effect of
ICRF plasma ionisation of the gas upon injection near the substrate.
10:40am C4-1-9 Electrical Transport in ZnO and ZnMgO Films: A
Comparison, K. Ellmer (ellmer@helmholtz-berlin.de), A. Bikowski, T.
Welzel, Helmholtz-Zentrum Berlin für Materialien und Energie, Germany
INVITED
Zinc oxide belongs to the material class of transparent conductive oxides
(TCO) which is both of scientific as well as technical interest, due to the
fact that TCO layers are used on a large scale for transparent electrodes in
many technical fields: flat panel displays, low emissivity glass coatings [1],
organic light emitting diodes (OLEDs) or thin film solar cells [2] . TCOs
are degenerately doped (N >> 10 19 cm -3 ) n-type compound semiconductors
with wide bandgaps (Eg > 3 eV) and low resistivities in the range of 10 -4 to
10 -3 Ωcm [3] . For its application as transparent electrodes they have to be
highly conductive and transparent at least in the visible spectral range. The
electron density N in ZnO is limited to about 1.5 . 10 21 cm -3 . Higher dopant
(electron) concentrations are not possible due to the formation of secondary
phases of the dopant and the host atoms. One goal is therefore to achieve a
low resistivity ρ = (eNµ) -1 by maximizing the mobility µ of the electrons.
The carrier transport in single-crystalline TCO semiconductors at such high
carrier concentrations is limited by ionized impurity scattering [4] . For the
application as transparent electrodes, however, polycrystalline TCO films
have to be used, which exhibit additional scattering processes: grain
boundary scattering and scattering at other crystallographic defects, further
reducing the electron mobility. ZnO alloys, like Zn1-xMgxO, are of scientific
interest, since the addition of other elements changes the band gap. With
respect to electrical transport, the so-called alloy scattering has to be taken
into account. In this paper the electrical transport in epitaxial and
polycrystalline ZnO and ZnMgO films is compared. For the film deposition,
magnetron sputtering as a well-known large-area deposition method is used.
Since in magnetron sputtering high-energetic negative ions (for instance O - )
occur, which can introduce crystallographic defects or interstitial oxygen
atoms, special emphasis is given to the radial variation of the electrical
properties and its correlation to the bombardment of the films by negative
ions. For this purpose, radially resolved ion distribution functions of
negative oxygen ions and other species at a growing film were measured,
both for new and eroded targets.
[1] J. Szczyrbowski, G. Bräuer, M. Ruske, H. Schilling, A. Zmelty, Thin
Solid Films 351 (1999) 254.
[2] K. Ellmer, A. Klein, B. Rech (Eds.), Transparent Conductive Zinc
Oxide: Basics and Applications in Thin Film Solar Cells, Springer, Berlin,
2008.
[3] T. Minami, MRS Bull. 25/8 (2000) 38.
[4] K. Ellmer, R. Mientus, Thin Solid Films 516/30 May (2008) 4620.
11:20am C4-1-11 Study of reactively Co-sputtered Sb-Sn oxide, G.
Ding (gding@intermolecular.com), M. Le, F. Hassan, Z. Sun, M. Ngugen,
Intermolecular Inc, US
Sb-Sn oxide (ATO) thin film was generated by reactively co-sputtered PVD
process on a flat glass. The film was characterized as the Sb contents and
annealing temperature, by transmission, reflection, absorption, resistivity,
film thickness, refractive index n and k, XRD,carrier density/mobility and
their gradience.The mechanism of those gradience are discussed
An ellipsometry method was developed to determine the ATO film carrier
density and gradience. There are some reports on the resistivity evaluation
based on the Drude model through ellipsometer measurements. However,
the uniqueness of the model fitting is poor in many conditions, (many
values could fit the model, so that no unique value could be precisely
determined). In theory: Tauc-Lorentz and Drude could give good
description of the band-gap and free carrier physics of the ellipsometry
spectra. The reason of poor uniqueness value in model fitting lies in that the
measurement data content is not enough to uniquely determine physical
parameters; thus the simulation will face uniqueness issue for the solution.
How to increase the measurement data content is a key to improve the
uniqueness of the simulation. Multiple angles did not help much on this data
content issue. The transmission and reflection spectra measurements were
helpful at some cases. However, the uniqueness is still poor in many other
cases in our ATO film study. Here we presented a new method that
combined resistivity measurement into modeling, instead of simulating
resistivity ρ. Thus, this method increases measurement data content, so it
significantly improved the uniqueness of the solution in the modeling; thus,
through Drude model relationship, the carrier density and mobility of the
ATO film could be uniquely determined.
The gradience profile simulation is widely used for ellipsometry simulation,
combined with the above method, the gradience of carrier density and
mobility can be estimated. In comparison of Hall probe measurements, two