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1109-B03-26

Nb-doped TiO2 films for transparent conductive electrodes with low resistivity deposited by dc magnetron sputtering using a TiO2-x–Nb2O5-x target Yasushi Sato1, Yuta Sanno1, Nobuto Oka1, Toshihisa Kamiyama2 and Yuzo Shigesato1 1 Graduate School of Science and Engineering, Aoyama Gakuin University, 5-10-1, Fuchinobe, Sagamihara, Kanagawa 229-8558, Japan 2 AGC Ceramics Co. Ltd., 5-6-1, Umei, Takasago, Hyogo 676-8655, Japan ABSTRACT Nb-doped anatase TiO2 films were deposited on unheated glass by dc magnetron sputtering using a slightly reduced TiO2-x–Nb2O5-x target with oxygen flow ratios [O2/(Ar+O2)] in the range from 0.00 to 0.20%. After postannealing in a vacuum (6 × 10-4 Pa) at 500 and 600 °C for 1 h, the films were crystallized into the polycrystalline anatase TiO2 structure. The resistivity of the both films decreased to 6.3-6.8 × 10-4 Ω·cm with increasing [O2/(Ar+O2)] to 0.10%, where the carrier density and Hall mobility were 1.9-2.0 × 1021 cm-3 and 4.9-5.0 cm2·V-1·s-1, respectively. The films exhibited high transparency of over 60-70% in the visible region of light. INTRODUCTION Since Furubayashi et al. reported epitaxially grown Nb-doped anatase TiO2 films deposited by pulse laser deposition [1], TiO2-based transparent conductive oxide (TCO) films have been investigated as indium-free alternatives to tin doped indium oxide (ITO) or indium zinc oxide (IZO), due to advantages of resource availability and non-toxicity compared to indium based TCOs. Hitosugi et al. reported that amorphous films were deposited on unheated glass by pulse laser deposition and the films postannealed at 500 °C under pure H2 gas at 1 atm had the lowest resistivity of 4.6 × 10-4 Ω·cm with optical transmittance of 60-80% [2]. For the production of large area commercial uniform TCO coatings, sputter deposition is the most promising deposition technique. Gillispie et al. reported an epitaxial Nb-doped anatase TiO2 film with a resistivity of 3.3 × 10-4 Ω·cm, which was deposited by rf magnetron sputtering using Nb-doped TiO2 targets [3]. Yamada et al. reported that amorphous films deposited on unheated glass by reactive sputtering and the postannealed at 600 °C under pure H2 gas at 100 kPa exhibited resistivity down to 9.5 × 10-4 Ω·cm with optical transmittance of 75% in the visible region [4]. It has also been reported that TiO2 films for optical coatings [5] and photocatalytic films [6] were deposited by dc magnetron sputtering using a slightly reduced TiO2-x target, where the deposition rate was 5-10 times higher than that by reactive sputter deposition using a Ti metal target. Oxidation of the TiO2-x target surface occurs gradually with increasing O2 flow ratio. Therefore, the TiO2-x target enables precise control of the degree of oxidation for TiO2 films deposited by sputtering under O2 flow ratio. We have reported that a Nb-doped TiO2 film with a resistivity of 1.3 × 10-3 Ω·cm was successfully deposited by dc magnetron sputtering using a TiO2-x target and Nb2O5 pellets [7]. In this study, Nb-doped TiO2 films were deposited