Effects of Zn Ratio Tuning on the Structural and Transport Properties of Amorphous Indium Zinc Tin Oxide Thin Films
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https://doi.org/10.1007/s11664-020-08502-2 2020 The Minerals, Metals & Materials Society
Effects of Zn Ratio Tuning on the Structural and Transport Properties of Amorphous Indium Zinc Tin Oxide Thin Films KE-DING LI1 and KAO-SHUO CHANG
1,2
1.—Department of Materials Science and Engineering, National Cheng Kung University, No.1, University Road, Tainan City 70101, Taiwan. 2.—e-mail: [email protected]
In this study, various indium zinc tin oxide (IZTO) films were fabricated using co-sputtering to explore amorphous transparent conducting oxides as alternatives to crystalline indium tin oxide (ITO). Various Zn ratios were tuned to study their effects on the structural evolution of IZTO. Amorphous IZTO (aIZTO) films were obtained when the Zn concentration was higher than approximately 17 at.%. X-ray diffraction and transmission electron microscopy analyses indicated that amorphous structures were formed due to the high crystallization temperatures of IZTO and nanocrystalline In2Zn5O8, which also caused aIZTO to exhibit small band gaps. On average, 87% transmittance was achieved in the visible light range. The aIZTO films had substantially higher transmittance in the infrared region than the ITO films did. Samples with Zn ratios between approximately 17 at.% and 27 at.% exhibited resistivity (approximately 3 9 10 4 X-cm), mobility (7 cm2 V 1 s 1), and carrier concentrations (4 9 1021 cm 3) comparable to those of crystalline ITO. Thus, the aIZTO films are promising alternative TCO materials. The mechanisms of competition between the crystallinity, oxygen deficiency, highmobility In2Zn5O8, and electron and hole generation rates were applied to shed light on the excellent electrical and transport properties of aIZTO films. Key words: Co-sputtering, amorphous indium zinc tin oxide, In2Zn5O8, optical property, hall measurement
INTRODUCTION Transparent conducting oxides (TCOs) are extensively applied in optoelectronic devices, such as liquid crystal and flat panel displays,1,2 organic light-emitting diodes (OLEDs),3 and photovoltaic solar cells,4 because they have superior optical transmittance in the visible light range and conductivity comparable to that of metals. Indium tin oxide (ITO) is a popular TCO with a band gap (Eg) of approximately 3.7 eV, low resistivity of 1 9 10 4 Xcm, and high transmittance of approximately 85%. However, ITO exhibits excellent characteristics only in its crystalline forms. Thus, high deposition temperatures or post-annealing (with temperatures
(Received January 31, 2020; accepted September 21, 2020)
of at least 200C) are typically required to fabricate products with desirable characteristics.5 The requisite high-temperature processes potentially preclude crystalline TCO from being applied to flexible substrates (e.g., polymers). Polycrystalline forms also lead to rough thin film surfaces, which may cause device failure due to inferior contacts with the contiguous layers and the formation of dark spots due to leakage currents.3 Low-temperature fabrication of amorphous TCOs (aTCO
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