Influence of Annealing Temperature on the Characteristics of Ti-Codoped GZO Thin Solid Film

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Hindawi Publishing Corporation Journal of Nanomaterials

Volume 2013, Article ID 502382,6pages http://dx.doi.org/10.1155/2013/502382

Research Article

Influence of Annealing Temperature on the Characteristics of

Ti-Codoped GZO Thin Solid Film

Tao-Hsing Chen and Tzu-Yu Liao

Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan Correspondence should be addressed to Tao-Hsing Chen; [email protected]

Received 6 May 2013; Accepted 29 June 2013 Academic Editor: Sheng-Rui Jian

Copyright © 2013 T.-H. Chen and T.-Y. Liao. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This study utilizes radio frequency magnetron sputtering (RF sputtering) to deposit GZO transparent conductive film and Ti thin film on the same corning glass substrate and then treats GZO/Ti thin film with rapid thermal annealing. The annealing temperatures

are 300∘C , 500∘C, and 550∘C, respectively. Ti:GZO transparent conductive oxide (TCO) thin films are deposited on glass substrates

using a radio frequency magnetron sputtering technique. The thin films are then annealed at temperatures of 300∘C, 500∘C, and

550∘C, respectively, for rapid thermal annealing. The effects of the annealing temperature on the optical properties, resistivity, and

nanomechanical properties of the Ti:GZO thin films are then systematically explored. The results show that all of the annealed films have excellent transparency (∼90%) in the visible light range. Moreover, the resistivity of the Ti:GZO films reduces with an increasing annealing temperature, while the carrier concentration and Hall mobility both increase. Finally, the hardness and Young’s modulus of the Ti:GZO thin films are both found to increase as the annealing temperature is increased.

1. Introduction

Transparent conductive oxide (TCO) thin films are widely used in the optoelectronics field for such applications as flat panel display devices, thin film solar cells, touch panels, and antistatic windows [1–5]. TCO films are commonly fabricated using tin-doped indium oxide (ITO) since ITO has a low resistivity (∼10−4_{Ω-cm) and excellent transmittance in the}

visible region [6–9]. However, ITO is both expensive (due to the limited availability of indium) and toxic. As a result, the problem of finding suitable alternatives for ITO has emerged as a pressing concern in recent years.

Zinc oxide (ZnO) has many favorable characteristics, including nontoxicity, low cost, high chemical and thermal stability, and good process integrability [10]. As a result, ZnO is regarded as a promising alternative to ITO in fabricating TCO thin-film structures. It has been shown that the electrical properties of ZnO can be enhanced by doping the lattice with aluminum (Al), gallium (Ga), or indium (In) [11]. Among these dopants, Al and Ga are particularly well suited to the fabrication of transparent conductive ZnO thin films because they contribute to electron conduction.

Al-doped ZnO thin films have high transmittance and low resistivity. However, Ga-doped ZnO thin films offer a number of practical advantages over Al-doped films, including a lower chemical reactivity, a greater resistance to oxygen, and a lower moisture resistance. Furthermore, the radius of Ga ions (0.062 nm) is closer to that of Zn ions (0.074 nm) than that of Al ions (0.053 nm) [12,13]. In addition, the covalent bond length of Ga-O (1.92 A) is smaller than that of Zn-O (1.97 A). As a result, minimal distortion of the doped ZnO lattice occurs, even in the case of a high Ga concentration. It has been shown that the addition of titanium (Ti) to the ZnO lattice is also of benefit in improving the electrical properties of ZnO thin films. However, the effects of Ti addition on the optoelectrical performance of Ga-doped ZnO (GZO) thin films have received little attention in the literature.

Many techniques are available for the deposition of ZnO-based films on different substrates, including spray pyrolysis [14], metal organic chemical vapor deposition (MOCVD) [15], reactive RF-magnetron sputtering [16], pulsed laser deposition (PLD) [17], thermal oxidation [18], molecular beam epitaxy (MBE) [19] and sol-gel [20]. Of these tech-niques, RF-magnetron sputtering is generally preferred for

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Journal of Nanomaterials 5 L o ad o n s am p le (mN) 12 8 4 0 0 100 200 300 Displacement (nm) GZO/Ti-room temperature GZO/Ti-RTA₃₀₀∘C GZO/Ti-RTA500∘C GZO/Ti-RTA550∘C (a) 0 100 200 300 Displacement (nm) H ar d ness (GP a) 10 8 6 4 2 0 GZO/Ti-room temperature GZO/Ti-RTA₃₀₀∘C GZO/Ti-RTA500∘C GZO/Ti-RTA550∘C (b) 0 100 200 300 Displacement (nm) GZO/Ti-room temperature GZO/Ti-RTA₃₀₀∘C M o d u lu s (GP a) 120 80 40 0 GZO/Ti-RTA500∘C GZO/Ti-RTA550∘C (c)

Figure 7: Nanomechanical response of as-deposited and annealed Ti:GZO thin films: (a) load displacement curves, (b) hardness curves, and (c) Young’s modulus curves.

Acknowledgment

The authors gratefully acknowledge the financial support provided to this study by the National Science Council (NSC) of Taiwan under Contract no. NSC 99-2218-E-151-006-MY2.

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