Improved crystallinity and optical properties of AlO x thin films by a ZnO interlayer
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To ascertain how the substrate influences the quality of AlOx films, AlOx films were grown on a bare glass and a ZnO-deposited glass in this study. By applying a ZnO interlayer before the AlOx deposition, AlOx films exhibited polycrystalline structure rather than amorphous as obtained by sputtering on a bare glass. For AlOx film on the ZnO-deposited glass, the transmission electron microscopy observation showed the coexistence of amorphous and polycrystalline structure, which reveals that the (122) plane in AlOx film is parallel to the surface of the substrate. The grains of the AlOx film grown on a ZnO-deposited glass comprising many small crystallites aggregated with sizes varying between 38 and 54 nm with irregular grain shapes. Besides, the ZnO interlayer with different deposition parameters had a significant effect in the diffusion interface between AlOx and ZnO. The ZnO interlayer could improve the optical transmission of AlOx films, especially when ZnO films are prepared with a high power of 200 W. Therefore, the glass/ZnO may be a good alternative substrate for producing high-quality AlOx films by controlling the epitaxial grain growth. The AlOx films grown on ZnO-deposited glasses have very good qualities in terms of crystallinity and optical properties.
I. INTRODUCTION
The most conventional oxide is the native alumina, which results from the exposure of aluminum metal to the atmosphere at room temperature. This oxide is approximately 2 nm thick and is amorphous.1 Aluminum oxide thin films have been produced by a variety of physical vapor deposition techniques2 such as direct current (dc) reactive sputtering,3 dual-pulsed dc magnetron sputtering,4 dc s-gun sputtering,5 and radio frequency (rf) sputtering.6 Ohring7 reported that aluminum oxide has a tendency to be amorphous when deposited as films. Schneider et al.2 also reported that aluminum-oxide coatings are x-ray amorphous when the substrate temperatures are below 300 °C. However, many of the desirable properties depend on the crystalline phases of aluminum oxide,8 such as high hardness, high abrasive and corrosion resistance,9 good thermal and chemical stability,10 and optical properties.2 In recent years there has been considerable research on the deposition of aluminum oxide films on a variety of substrates because of several applications of the oxide films11 in industry. To investigate the influence of crystallinity, AlOx films were directly grown on both bare
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e-mail: [email protected] J. Mater. Res., Vol. 18, No. 4, April 2003
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glass and ZnO-deposited glass substrates in this study. ZnO film is attractive because it has a preferential growth along the c-axis, which was previously reported.12 ZnO was recently found to be a good buffer layer for the growth of gallium nitride and a room-temperature lasing material.13 In this study, the ZnO layer was deposited by rf magnetron sputtering on a glass substrate. After the deposition, the metallic Al film was further deposited on ZnO by d
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