Characterization and optoelectronic properties of sol-gel-derived CuFeO₂ thin films

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• 作者：Hong-Ying Chen ; ^{hychen@cc.kuas.edu.tw} ; Jia-Hao Wu
• 关键词：Transparent conductive oxide ; Sol&ndash ; gel deposition ; Thin films ; Delafossite ; Copper iron oxide ; Annealing ; X-ray diffraction
• 刊名：Thin Solid Films
• 出版年：2012
• 期刊代码：78_00406090
• 类别：ph
• 出版时间：31 May, 2012
• 卷：520
• 期：15
• 页码：5029-5035
• 文件大小：1102 K

摘要

In this study, CuFeO₂ thin films were deposited onto quartz substrates using a sol-gel and a two-step annealing process. The sol-gel-derived films were annealed at 500 掳C for 1 h in air and then annealed at 600 to 800 掳C for 2 h in N₂. X-ray diffraction patterns showed that the annealed sol-gel-derived films were CuO and CuFe₂O₄ phases in air annealing. When the films were annealed at 600 掳C in N₂, an additional CuFeO₂ phase was detected. As the annealing temperature increased above 650 掳C in N₂, a single CuFeO₂ phase was obtained. The binding energies of Cu-2p_3/2, Fe-2p_3/2, and O-1s were 932.5 卤 0.1 eV, 710.3 卤 0.2 eV and 530.0 卤 0.1 eV for CuFeO₂ thin films. The chemical composition of CuFeO₂ thin films was close to its stoichiometry, which was determined by X-ray photoelectron spectroscopy. Thermodynamic calculations can explain the formation of the CuFeO₂ phase in this study. The optical bandgap of the CuFeO₂ thin films was 3.05 eV, which is invariant with the annealing temperature in N₂. The p-type characteristics of CuFeO₂ thin films were confirmed by positive Hall coefficients and Seebeck coefficients. The electrical conductivities of CuFeO₂ thin films were 0.28 S cm^鈭?#xA0;1 and 0.36 S cm^鈭?#xA0;1 during annealing at 650 掳C and 700 掳C, respectively, in N₂. The corresponding carrier concentrations were 1.2 脳 10¹⁸ cm^鈭?#xA0;3 (650 掳C) and 5.3 脳 10¹⁸ cm^鈭?#xA0;3 (700 掳C). The activation energies for hole conduction were 140 meV (650 掳C) and 110 meV (700 掳C). These results demonstrate that sol-gel processing is a feasible preparation method for delafossite CuFeO₂ thin films.