Influence of Al content and annealing atmosphere on optoelectronic characteristics of Al:ZnO thin films
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Influence of Al content and annealing atmosphere on optoelectronic characteristics of Al:ZnO thin films Feng‑Kuan Chen1 · Du‑Cheng Tsai1 · Zue‑Chin Chang2 · Erh‑Chiang Chen1 · Fuh‑Sheng Shieu1 Received: 30 April 2020 / Accepted: 21 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Aluminum-doped zinc oxide (AZO) was cosputtered from ZnO and Al targets on glass substrates at room temperature. The effect of Al-target power and annealing atmosphere on structural and optoelectronic properties of AZO films was investigated.[Al]/[Zn] ratio increased to 0.258 when the Al-target power increased to 250 W. At a fixed Al-target power of 200 W, the [Al]/[Zn] ratio was 0.104 and the as-deposited AZO film demonstrated a low resistivity of 3.19 × 10−4 Ω-cm and high transmittance of approximately 90% in the visible region. After annealing at 500 °C in forming gas (5% H 2 in Ar) atmosphere, the resistivity of the AZO film can be further reduced to 9.38 × 10−5 Ω-cm. Given its low-temperature process and good optoelectronic properties, sputtered AZO films that use ZnO and Al targets have high potential in various optoelectronic devices. Keywords Transparent conducting oxide · Aluminum-doped zinc oxide · Co-sputtering · Electronic properties · Annealing atmosphere
1 Introduction Transparent conducting oxide (TCO) thin films are commonly used as transparent electrodes in touch panels, flatpanel displays, and solar cells. Tin-doped indium oxide (ITO) is a commonly used TCO material because of its high transmittance in the visible region and low electrical resistivity [1]. However, toxicity and high cost of ITO are major disadvantages in commercial production. A viable alternative to ITO must be developed. During the last 2 decades, aluminum-doped zinc oxide (AZO or ZnO:Al) has attracted increasing attention from researchers as a viable alternative to ITO, because AZO and ITO have similar electrical and optical properties. Moreover, compared with ITO, AZO is a nontoxic and inexpensive material with high-temperature stability.
* Fuh‑Sheng Shieu [email protected] 1
Department of Materials Science and Engineering, National Chung Hsing University, Taichung 40227, Taiwan, Republic of China
Department of Mechanical Engineering, National Chin-Yi University of Technology, Taichung 41170, Taiwan, Republic of China
2
Many groups have investigated the optical and electrical properties of ZnO thin films by doping them with Al, Mg, Co, Ga, Sn, S, and Cu elements. Among the dopants in ZnO, Al is highly suitable because of its easy availability, low cost, ease of doping, and superior properties. Moreover, compared with Z n 2+ (0.074 nm), the smaller ionic radius (0.053 nm) of highly reactive Al improves the efficiency in crystallographic substitution of Al atom for Zn atom at ZnO lattice site [2,3]. Al–O (1.810 Å) and Zn–O (2.009 Å) bonds have comparable lengths, which result in the smallest amount of disorder [3,4]. However, optoelectronic properties of AZO films are highly perceptive to deposi
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