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日
期：2010.10.04
指導老師：林克默 博士
學
生：陳冠廷
Outline
1. Introduction
2. Experimental
3. Results and discussion
4. Conclusions
1.Introduction
•
Solution growth techniques such as the sol–gel method have been receiving high
attention since it enables us to develop low-cost and simple deposition procedure
to obtain large area high quality AZO films for technological applications.
•
In this study, we focus on discussing the formation process of microstructure as
well as its influences on the film properties and try to understand the kinematic
mechanism.
2. Experimental details
•
Zinc acetate dihydrate was used as a starting material, lsopropylalcohol and
aluminumnitrate served as the solvent and dopant sources, respectively.
•
The Al/Zn ratio in the solution was varied from 1% to 4%. The solution
concentration was 0.3 and 0.5 mol/l.
•
After being deposited on glass (corning 1737) by dip-coating, the films were first
dried at 70 °C for 10 min. Afterwards, the films were heated in a furnace at 500–
700 °C for 1 h in air (pre-heat treatment).
•
The procedures from coating, drying, to annealing were repeated 2–5 times so
that the sintered film thickness could be up to 400 nm.
•
These films were then annealed in vacuum (∼ 1 mtorr) at 500–700 °C for 1 h (postheat treatment).
3 .Results and discussion
Fig. 1. X-ray diffraction patterns of AZO films in dependence of the
number of layers, 0.5 mol/l, Al/Zn=1 at.%.
Fig. 2. The relative intensity changes of the (002) peaks indicated that the
preferred growth orientation of ZnO crystal was restrained by the film itself.
Fig. 3. Due to the growth mechanism, the samples‘ crystallite size
grew slightly along with the increasing number of film layers. In
contrast, the Al concentration affected the crystallite size
considerably.
Fig. 4. Samples‘ lattice deformation versus layer number; the
samples were preheated by 600 °C in air, and post heated by
600 °C under vacuum (∼1 mtorr).
Fig. 5. Film resistivity versus layer number under different
procedure conditions. Pre-heat treatment 600 °C, 0.3 mol/l
open symbols, 0.5 mol/l closed symbols.
Fig. 6. Carrier concentration, mobility and crystallite size
versus layer number, 0.5 mol/l, Al/Zn=1 at.%.
Fig. 7. Comparison of film transmittances, 5 layers.
Fig. 8. Band gap energies versus layer number.
4. Conclusion
•
In this study, it was found that the c-oriented growth of ZnO crystal was disturbed
during the multi-layered dip-coating process. This process did not enable the
crystallite size to grow obviously, but it could allow crystallite and Al atoms to find
the suitable positions and led to a better film quality.
•
The change of the microstructures affected the carrier concentration more
considerably than the carrier mobility. The latter one was mainly influenced by the
dopant concentration. The higher dopant concentration led to smaller crystallite
size.
•
We also found that the effective Al concentration of AZO films was much lower
than the dopant concentration. This agreed well with the measured carrier
concentration. It means that most of the Al atoms did not replace the lattice
positions of the Zn atoms.
•
Thus, we believe that film conductivity can be enhanced by way of the well
directed growth and the controlling of the dopant distribution. In addition, the
optical measurements showed that along with the increasing film thickness, the
band gaps of the transparent films gradually approached the theoretical value of
ZnO.
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