Thickness dependence of microstructural evolution of ZnO films deposited by rf magnetron sputtering
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Thickness dependence of microstructural evolution of ZnO films deposited by rf magnetron sputtering Yong Eui Leea) Inter-University Semiconductor Research Center (ISRC) and School of Material Science and Engineering, Seoul National University, Seoul 151-742, Korea
Young Jin Kim Department of Elec. and Advanced Materials Engineering, Kyonggi University, Suwon 440-760, Korea
Hyeong Joon Kim Inter-University Semiconductor Research Center (ISRC) and School of Material Science and Engineering, Seoul National University, Seoul 151-742, Korea (Received 27 January 1997; accepted 26 December 1997)
The microstructural evolution, including preferred orientation and surface morphology, of ZnO films deposited by rf magnetron sputtering was investigated with increasing film thickness. Preferred orientation of the ZnO films changed from ¢ ° ¢ ° s0002d ! 1011 ! 1120 , and fine and dense columnar grains also changed to large elongated grains with increasing thickness. Such selective texture growth was explained with an effect of highly energetic species bombardment on the growing film surface. The relationship between preferred orientation change and microstructural evolution was also discussed.
I. INTRODUCTION
Preferred orientation, which is a phenomenon that a certain crystal plane grows parallel to a substrate, is one of the most important properties in thin films. Along with a microstructure it is very important to control the preferred orientation for device applications. In a growing of ZnO thin films which belong to tetrahedrally coordinated II–VI compounds, it is primarily important to control the preferred orientation for each application. For example, films must have high c-axis preferred orientation for application of longitudinal bulk wave transducers and surface acoustic wave (SAW) filters using a Rayleigh wave.1 While the c-axis of the films was inclined normal to the substrate or parallel to the substrate for shear wave transducers and SAW filters using Sezawa wave.2 It was also reported that only the films having c-axis parallel to the substrate revealed photocurrent phenomena.3 Up until now, numerous articles have been reported for the preparation and characterization of the ZnO thin films having high c-axis preferred orientation. Their research was mainly focused on optimization of deposition conditions. However, there has been no systematic study in which one attempts to understand the mechanism of the preferred orientation in ZnO thin films. There were few reports for the preferred orientation change and the microstructural evolution with thickness. a)
Present address: Ceramic Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899.
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 5, May 1998
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In this article, we investigated the microstructural evolution and the preferred orientation change of the ZnO films with varying their thickness and have tried to show the correlation of crystallogr
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