Deposition of F-doped ZnO transparent thin films using ZnF 2 -doped ZnO target under different sputtering substrate temp
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NANO EXPRESS
Open Access
Deposition of F-doped ZnO transparent thin films using ZnF2-doped ZnO target under different sputtering substrate temperatures Fang-Hsing Wang1, Cheng-Fu Yang2* and Yen-Hsien Lee1
Abstract Highly transparent and conducting fluorine-doped ZnO (FZO) thin films were deposited onto glass substrates by radio-frequency (RF) magnetron sputtering, using 1.5 wt% zinc fluoride (ZnF2)-doped ZnO as sputtering target. Structural, electrical, and optical properties of the FZO thin films were investigated as a function of substrate temperature ranging from room temperature (RT) to 300°C. The cross-sectional scanning electron microscopy (SEM) observation and X-ray diffraction analyses showed that the FZO thin films were of polycrystalline nature with a preferential growth along (002) plane perpendicular to the surface of the glass substrate. Secondary ion mass spectrometry (SIMS) analyses of the FZO thin films showed that there was incorporation of F atoms in the FZO thin films, even if the substrate temperature was 300°C. Finally, the effect of substrate temperature on the transmittance ratio, optical energy gap, Hall mobility, carrier concentration, and resistivity of the FZO thin films was also investigated. Keywords: Deposition; FZO thin films; Secondary ion mass spectrometry
Background Transparent conducting oxide (TCO) thin films based on zinc oxide (ZnO) are promising for applications in various optoelectronic devices. In spite of extensive studies on preparation, characterization, and effect of doping on the properties of ZnO, certain effects of either some dopant or preparation procedures are still remaining unclear. However, ZnO-based thin films present a lot of advantages such as low material cost, non-toxicity, and high chemical stability under the hydrogen plasma as compared to tin-doped indium oxide (ITO) [1]. For that, transparent conducting ZnO thin films have already been extensively used in solar cells, light-emitting diodes, and liquid crystal displays as a substitute for ITO [2,3]. Much more interest has been given to TCOs based on ZnO such as undoped ZnO thin films [4], Al-doped ZnO (AZO) thin films [5], and Ga-doped ZnO (GZO) thin films [6] due to their stability under hydrogen plasma which makes them a potential candidate for solar cells' technology based on thin-film silicon. Fluorine, the ionic radius (0.136 nm) * Correspondence: [email protected] 2 Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 81148, Taiwan Full list of author information is available at the end of the article
of which is similar to that of oxygen (0.132 nm), may be an adequate anion doping candidate due to lower lattice distortion compared with Al, Ga, and In, but comparatively few studies on fluorine-doped ZnO (F-doped ZnO) can be found in the past researches [7]. Many different physical and chemical deposition methods were used to investigate the properties of the F-doped ZnO thin films. For example, the F-doped ZnO thin films were deposited on Corning glass
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