日 期： 2010.10.04 指導老師：林克默 博士 學 生：陳冠廷. outline 1.introduction...

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 (post-heat 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 thepreferred 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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