報 告 人：王禮國 指導老師：林克默 博士 日 期：

Outline 1. Introduction 2. Experimental procedure 3. Results and discussion 4. Conclusions 2

Introduction Transparent conductive Al-doped ZnO films were deposited by the sol–gel method. The growth mechanism of the film microstructure and its influences on the electrical properties were discussed. Zinc oxide and doped zinc oxide films have received extensive attention in recent years due to their excellent optical and electrical properties. Several deposition methods such as sputtering technique pulsed laser deposition,thermal plasma,MOCVD,spray pyrolysis and sol–gel method have been investigated and compared for deposition of the AZO films. 3

Experimental procedure In our experiments, Zinc acetate dihydrate was used as a starting material,lsopropyl alcohol and aluminum nitrate 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 by dip-coating,the films were first dried at 70 °C for 10 min to evaporate the solvent partially.After wards, 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). 4

X-ray diffraction patterns of AZO films in dependence of the number of layers, 0.5 mol/l, Al/Zn=1 at.%. 5 The relative intensity changes of the (002) peaks indicated that the preferred growth orientation of ZnO crystal was restrained by the film itself.

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. 6 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.

Comparison of film transmittances, 5 layers. 7 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).

Conclusions 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 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 Alatoms 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. 8

Thank you for your attention 9