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Electrical and optical properties of Aldoped ZnO
thin films by sol–gel process
Young-Sung Kim a, Weon-Pil Tai b,*
教授:林克默博士
學生:董祐成
日期:2011/5/23
2016/7/13
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Outline
•
•
•
•
Introduction
Experimental
Result and Discussion
Conclusion
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Introduction
• In the present study, Al-doped ZnO (AZO) films
were prepared on glass substrate by the sol–gel
spin coating method using homogeneous and
stable zinc acetate dihydrate-isopropanolmonoethanolamine sol doped with 1 at.% Al with
respect to Zn.
• The crystal orientation, electrical and optical
properties
with
post-deposition
heating
temperature were investigated.
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Experimental
• Zinc acetate dehydrate (Zn(CH3COO)22H2O) and
aluminum chloride hexahydrate (AlCl36H2O)
were dissolved in a solution of isopropanol and
monoethanolamine.
• The molar ratio of MEA to zinc acetate was 1.0
and the concentration of zinc acetate was 0.7
mol/l.
• The concentration of Al as a dopant was of 1.0
at.% with respect to Zn.
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• The resultant solution was stirred at 50℃ for 1 h
to yield a clear and homogeneous solution.
• The solution was finally aged at room
temperature for 24 h. Al-doped ZnO (AZO) films
were prepared on glass (Corning Inc. 7059)
substrate by repeated coating.
• Spin coating was performed at room temperature,
with a rate of 3000 rpm for 20 s.
• After depositing each times, the films were
preheated
in
air
at
275
℃
for
10
min.
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• After repeating the coating procedure five times
for the final film thickness of approximately 250
nm, the films were finally postheated at 500, 550,
600, 650 and 700 ℃ for 1 h in air using an
electronic furnace.
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Result and Discussion
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• Fig. 1 shows surface morphologies of AZO films
preheated at 275 ℃ and postheated at 500–700
8C with an interval of 50 ℃.
• The AZO films were deposited on glass
substrates by the spin coating method. The films
possess the crystalline size of nanometer order
having uniform and dense microstructure. The
crystalline size increases with increasing postdeposition heating temperature from 500 to 700
℃.
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• The crystalline greatly grows at the postdeposition heating temperature of 700 ℃ and the
pores in the surface were partly formed by the
coalescence of microvoids. It indicates that the
pores in the surface are related with the
decomposition reaction of the precursor and the
evaporation of residual organics in gel films
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• The post-deposition heating temperature greatly
affected the crystal orientation of the ZnO films
fabricated by dip-coating . The undoped ZnO
films prepared using isopropanol solvent
appeared the peaks of the (1 0 0) and (1 0 1)
planes in addition to the (0 0 2) plane .
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• However, the ZnO films doped with 1 at.% Al
show a preferred orientation along the (0 0 2)
plane. It means that the doping of small amount
of Al in the ZnO film promotes c-axis orientation
even though a solvent of low boiling point,
isopropanol is used. Moreover, the ZnO film
doped above 2 at.% Al decreased c-axis
orientation
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• The crystallite size increases from 14 to 28 nm
with increasing the post-deposition heating
temperature from 500 to 700 ℃. This exhibits a
similar tendency as obtained from the SEM, as
shown in Fig. 1.
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Optical transmittance spectra (a) and (ahn) vs. hn plot based on the transmittance spectra (b) of Al-doped ZnO films postheated at various
temperatures.
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• Fig. a) shows optical transmittance spectra of the AZO
films in the wavelength range of 250–800 nm. All the
films were highly transparent in the visible region. The
optical transmittance in the visible range was 86–91%,
but slightly decreased in the film postheated at 700 ℃.
• The ZnO films with higher c-axis orientation have
higher optical transmittance.In this study, the AZO film
postheated at 700 ℃ havelow optical transmittance even
though it exhibits the highestc-axis orientation. The low
transmittance is due to thesegregated Al2O3 and pores
formed in the AZO film during post-deposition heating.
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• The optical band gap increases with increasing
post-deposition heating temperature and the
value is found to be 3.24–3.28 eV.
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Resistivity of Al-doped ZnO films postheated at various temperatures
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• The higher the c-axis preferred orientation the lower the
resistivity due to the reduction in the scattering of the
carriers at the grain boundaries.
• owever, the electrical resistivity increases considerably
in the film postheated at 700 ℃, which lead to the
segregation of Al2O3 at grain boundaries and partially
pores. The large increase of resistivity in the AZO film
postheated at 700 ℃ may be due to decrease in carrier
mobility by segregation of Al2O3 at grain boundaries
and partially pores.
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Conclusion
• 玻璃基板上使用溶膠凝膠旋塗法製備了鋁摻
雜氧化鋅薄膜，對其熱退火後電性及光性進
行了研究。
• 電阻率在後退火溫度700 ℃時上升。穿透率再
後退火溫度 650 ℃時超過86％，但在700 ℃時
下降。其惡化的電學和光學性能的原因是
在AZO薄膜後退火溫度700 ℃時似乎是Al2O3
在晶界和部分孔隙被隔離所致。
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THANKS FOR YOUR
ATTENTION
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