Upgrading the Triboluminescence of ZnS:Mn Film by Optimization of Sputtering and Thermal Annealing Conditions
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C.N. Xua) National Institute of Advanced Industrial Science and Technology, AIST, Kyushu, Shuku 807-1, Tosu, Saga 841-8502, Japan
M. Suzuki and X.G. Zheng Department of Physics, Saga University, Saga 840-8502, Japan (Received 24 November 2001; accepted 15 January 2002)
A statistical method of the design of experiments and analysis of variance (ANOVA) was used to obtain optimized sputtering conditions for oriented ZnS thin films doped with 5% manganese on glass substrates. The effects on the five sputtering factors—substrate temperature, radio frequency power, sputtering pressure, sputtering time, and pre-sputtering time—were simultaneously investigated by using the design of experiments and ANOVA. Through only 16 experiments, it was proved statistically at the 5% level that the substrate temperature was the only significant control factor. ZnS films were then deposited under the optimized sputtering conditions on fused quartz and thermally annealed in a reducing ambient (5% H2 diluted in Ar) at 500, 600, 700, and 800 °C. It was found that the crystallinity and triboluminescence intensity of the films were enhanced by postannealing up to 700 °C.
I. INTRODUCTION
ZnS, a II-IV semiconductor, has many applications in various fields, such as phosphors,1 solar cells,2 and infrared windows.3 Films of ZnS doped with Mn (ZnS:Mn) are used as the active layers of both alternating and direct current thin film electroluminescence (TFEL) devices.4,5 Besides these optoelectric applications, we are also interested in the new mechano-optic applications because ZnS:Mn film is a promising material to emit intense light upon stress,6 a phenomenon known as triboluminescence (TrL).7–10 Many materials exhibit TrL, however the emitted light in most materials is too weak to detect. In previous studies,11,12 the crystallinity and luminescence properties of ZnS:Mn films grown by ion plating were improved by postannealing at higher temperatures. Various chemical and physical vapor methods can be used to prepare ZnS:Mn films; among them radio frequency (rf) magnetron sputtering is an attractive production technique.13 Using this technique, the crystallinity of the films greatly depends on many sputtering factors such as substrate temperature, rf power, etc. Thus the optimization of
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 5, May 2002
sputtering conditions requires a large number of experiments. Design of experiments and analysis of variance (ANOVA) are mathematical statistical methods that will reduce the number of experiments, show the effect of a control factor, and then give the optimum sputtering conditions.14,15 For example, to investigate 5 sputtering control factors with 4 levels (45), only 16 experiments (L16) would be sufficient to obtain the optimum sputtering conditions by using design of experiments L16 (45) and ANOVA. In this study, we investigated the significance of 5 sputtering factors—substrate temperature, rf power, sputtering pressure, sputtering time, and pre-
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