Electrical and Structural Properties of Ta-doped SnO 2 Transparent Conductive Thin Films by Pulsed Laser Deposition
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Electrical and Structural Properties of Ta-doped SnO2 Transparent Conductive Thin Films by Pulsed Laser Deposition Shoichiro Nakao1, 2, Naoomi Yamada3, Yasushi Hirose1, 2, 4 and Tetsuya Hasegawa1, 2, 4 1 Kanagawa Academy of Science and Technology (KAST) 3-2-1 Sakado, Kawasaki, Kanagawa 213-0012, Japan 2 Japan Science and Technology Agency, CREST 7-3-1 Hongo, Tokyo 113-0033, Japan 3 Department of Applied Chemistry, Chubu University 1200 Matsumoto, Kasugai, Aichi 487-8501, Japan 4 Department of Chemistry, The University of Tokyo 7-3-1 Hongo, Tokyo 113-0033, Japan ABSTRACT We investigated electrical and structural properties of Ta-doped SnO2 (TTO) films on anatase TiO2 seed layers with various growth parameters of pulsed laser deposition. We found that anatase TiO2 seed layers induced pseudo-epitaxial (100) growth of TTO films with enhanced mobility (µ) in a wide range of growth parameters. The highest µ of 83 cm2V-1s-1 [resistivity (ρ) of 2.8 × 10-4 Ωcm] and the lowest ρ of 1.8 × 10-4 Ωcm (µ of 60 cm2V-1s-1) were obtained at a substrate temperature of 600 °C. Amorphization and (101)-preferred growth competed with (100) growth on the TiO2 seed layer at low temperatures. Introducing sufficient process oxygen suppressed such unwanted film growth, resulting in improved transport properties. INTRODUCTION Transparent conductive oxides (TCOs) are key materials for electrodes of optoelectronics such as flat panel displays, light-emitting diodes, and photovoltaics. Among various materials, SnO2 is one of the most important TCOs due to excellent chemical stability, wide optical gap, and low material cost. In particular, F-doped SnO2 (FTO) films by chemical vapor deposition (CVD) have been widely utilized for coatings of low-emissivity glass and electrodes of photovoltaics. In contrast to vast industrial use of CVD films, however, physical vapor deposition (PVD) such as sputtering and pulsed laser deposition (PLD) have been rarely used to deposit SnO2 films. That is because, empirically, low resistivity (ρ) is difficult to achieve in SnO2 films by sputtering [1]. Recently, however, Toyosaki et al. have reported that epitaxial Ta-doped SnO2 (TTO) films grown on rutile TiO2 single crystal substrates by PLD exhibited excellent conductivity with ρ of 1.1 × 10-4 Ωcm [2]. Furthermore, we have reported that similar low ρ of 1.8 × 10-4 Ωcm can be achieved in TTO films even on glass substrates with the aid of seed layer [3]. The use of 10nm-thick anatase TiO2 seed layer promoted pseudo-epitaxial growth TTO films with (100) orientation. The pseudo-epitaxial growth significantly reduced grain boundary scattering, resulting in dramatic improvement of transport properties. Moreover, we have demonstrated that the use of seed-layer effectively reduces ρ of sputtered films as well as PLD ones [4]. Here, we present detailed electrical and structural properties of TTO films with various growth parameters of PLD. We found that TiO2 seed-layers induce pseudo-epitaxial (100) growth of TTO films with enhanced mobility in a wide range of growth parame
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