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Highly stable transparent and conducting
gallium-doped zinc oxide thin films for
photovoltaic applications
E. Fortunato , L.Raniero,L.Silva,A.Gonc-alves,A.Pimentel,P.Barquinha,H.A´guas, L.Pereira, G. Goncalves,I.Ferreira,E.Elangovan,R.Martins
CENIMAT/I3N,MaterialsScienceDepartment,FCT-UNLandCEMOP-UNINOVA,CampusdeCaparica,2829-516Caparica,Portugal
教授:林克默博士
學生:董祐成
日期:2011/04/11
2016/7/13
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Outline
•
•
•
•
Introduction
Experimental
Result and Discussion
Conclusion
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Introduction
• Transparent conducting oxide (TCO) with an optical
transmission exceeding 80% in the visible region (500–
650nm) and a resistivity less than 10-3 Ωcm have been
widely used inavariety of applications for more than a
half-century.
• However , most of these techniques require moderate
substrate temperatures to obtain low resistivity . Among
the available techniques, RF magnetron sputtering
presents several advantages including the production of
highly transparent and conducting gallium zinc oxide
(GZO) without heating the substrate.
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Experimental
• The GZO films were deposited initially on soda lime
glass substrates by RF (13.56MHz) magnetron
sputtering using a 5cm planar ceramic oxide target
consisting ZnO (98wt%):Ga2O3 (2 wt%) from Super
Conductor Materials, Inc. with a purity of 99.99%.
• The sputtering was carried out at RT with an argon
deposition pressure of 0.15Pa. The substrate–target
distance (10cm) and the RF power (175W) were
maintained constant for all depositions. The typical
growth rate for these deposition conditions is 30 nm/min.
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• The deposition conditions optimized from the GZO films
deposited on glass substrates were later used to deposit the
GZO films on polyethylene naphthalate (PEN) substrates.
The PEN substrates possess high stiffness, low thermal
shrinkage, and high chemical resistance.
• The film thickness was measured using a surface
profilometer (Dektak 3D from Sloan Tech.). The surface
morphology was analyzed using a field effect scanning
electron microscope (FE-SEM,S-1400 Hitachi) . The
electrical resistivity (ρ), free carrierconcentration (N) and
Hall mobility (μ) were inferred by the four point probe
method and Hall effect measurements in van der Pauw
geometry (Biorad HL5500) at a constant magnetic field of
0.5T.
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• X-ray diffraction measurements were performed using
Cu-Ka radiation (Rigaku DMAX III-Cdiffractometer) in
Bragg–Brentanogeometry(θ/2θcoupled).
• The optical transmittance measurements were performed with a Shimadzu UV/VIS 3100 PC double beam
spectro-photometer in the wavelength range from 300 to
2500 nm.
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Result and Discussion
Dependence of the electrical resistivity (ρ), carrierconcentration (N) and Hall mobility
(μ) as a function of film thickness of the GZO films deposited at room temperature
(inthisstudy).
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• A maximum bulk resistivity (ρ) of ~ 5.7×10-4Ωcm
obtained for the 100 nm thick films was decreased with
the increasing film thickness to reach a minimum of ~
2.8×10-4Ωcm at 1100nm.
• We have observed a continuous increase on the mobility
(μ) as the thickness increases (from 11 to 18
cm2/Vs) .This behavior can be attributed to a reduction
in the ionized impurity scattering and or an increase in
the crystallite size.
• However , we notice that ρ tends to saturate for
thicknesses above 500 nm . Similar results have been
obtained for Al-doped
ZnO.
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XRD patterns obtained from the GZO films deposited with different thicknesses (inset
shows the pattern from the thickest sample).
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• For all the films , only the ZnO (002) peak at 2θ =
34.31° is observed revealing that the films are
polycrystalline with a hexagonal structure and a
preferred orientation along the c-axis perpendicular to
the substrate.
• As the thickness increases the peak intensity
corresponding to the plane (002) increases significantly ,
whereas the peak width decreases.
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Dependence of Hall mobility of the GZO films with the crystallite size (data obtained through
Scherrer’s formula).
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• A linear dependence between the mobility and the
crystallite size was obtained through the equation , μ
=k+0.5983dc, where k is a constant and dc is
crystallitesize.
• This is consistent with the previous results since the
mobility is mainly dependent on the grain boundary
scattering and lattice defects, which decrease with the
increase of the crystallite size.
• This also suggests that the only way to decrease the
resistivity is by increasing the mobility .
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Surface SEM micrographs (with 40° tilt angle) of GZO films deposited at room temperature, with
different thicknesses
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• Shows two typical SEM micrographs of GZO films with
a low (110nm) and high (1110nm) film thicknesses
respectively,with an apparent viewing angle of 40 °
• The surface roughness is increased with the increasing
film thickness, suggesting an enhancement of the grain
size as already confirmed by the electrical and X-ray
diffraction measurements.
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Optical transmittance obtained from the GZO films as a function of film thickness.
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• shows the optical transmittance vs. wavelength in the
visible and near-infrared region obtained from the films
with thicknesses ranging from 110 to 1100 nm.
• The near-infrared transmittance decreases as the film
thickness increases, whereas the average transmittance
at the visible range is obtained as 80% and 90% from
the low and high thickness films, respectively. These
changes in the optical properties are consistent with the
changes observed in the electrical, structural and
morphological properties.
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Conclusion
• 從本篇可知，如要獲得高穿透性的透明薄膜，
可用射頻磁控濺射在室溫下沉積GZO。
• 薄膜的結晶結構、表面形貌與電性都取決於
膜厚。
• 本篇做出來的最低的電阻率接近2.8×10-4、遷
移率接近18而穿透率則是超過80%。
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THANKS FOR YOUR
ATTENTION
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