Combinatrial study for Mg-Si thin films fabricated by RF co-sputtering with Mg and Si targets
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Combinatrial study for Mg-Si thin films fabricated by RF co-sputtering with Mg and Si targets Y. Morita1, Y. Hayashi1, H. Tsuchiura2, M. Nishitani1 1 Graduate School of Engineering, Osaka University, Suita, Osaka, JAPAN 2 Department of Applied Physics, Tohoku University, Sendai, JAPAN ABSTRACT Mg-Si thin films were systematically studied using combinatorial approach by co-sputtering with Mg and Si targets. Single phase of Mg2Si appeared around the stoichiometric composition region, and in Mg-rich region (Mg/Si>4) Mg2Si and Mg phases coexisted. The transition of electrical conduction type from n-type to p-type occurred near the stoichiometric composition region where the strongest peak of Mg2Si appeared in the XRD patterns and the Raman scattering spectra. The p-type conduction was observed in Mg-poor region near the stoichiometric composition region. The results of first principle calculation suggest that Mg vacancy may cause p-type conduction. INTRODUCTION Magnesium silicide (Mg2Si) has attracted much attention in view of its potential application in thermoelectric generators, infrared sensors, and solar photovoltaic cells. Recently, Mg2Si thin films have significant interest for applications in thin film devices on flexible substrates and hybrid devices such as thermoelectric generator and solar photovoltaic cells. On the other hand, fewer reports were published about fundamental properties of Mg-Si thin films.1-4 Tani et al. reported the deposition of Mg-Si thin films by RF magnetron sputtering using an elemental composite target composed of Si chips on a Mg disk.3 Only n-type conduction was observed by Hall effect measurements in deposited films which have various compositions. On the other hand, Ogawa et al. reported p-type conduction of Mg2Si films deposited RF magnetron sputtering. 4 These reports indicate that Mg-Si films show characteristic behavior in electrical conduction for its composition and sputtering condition. The control of the conduction type of films is very important for thin film devices. In this work, in order to understand the fundamental properties of Mg2Si thin films, Mg-Si thin films were systematically studied using combinatorial approach by RF co-sputtering with Mg and Si targets. XPS, XRD and Raman scattering measurements were used to characterize the deposited films. EXPERIMENTAL DETAILS RF co-sputtering was used to fabricate continuous composition gradient on quartz glass at 573K with Mg (99.9% purity) and Si (99.99% purity) targets. The sputtering powers were 40W and 30W for Mg and Si targets, respectively. The background pressure before introducing (Ar+H21%) gas was 10-5 Pa and the working pressure was 8.0 Pa during the deposition. The dimension of the quartz glass is 20mm x 30mm x 1mm. The thickness of deposited film
estimated by SEM cross-section images was about 2 micrometer for the deposition of 5 hours. The deposited Mg-Si film was annealed in vacuum at 773K for 10min. After post annealing, structural and electronic properties of the film were measured. The film composition
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