Journal of the Korean Physical Society, Vol. 54, No. 2, February 2009, pp. 944949
Enhanced Electrical and Optical Properties of Atmospheric-Plasma-Treated Al-Doped ZnO Thin Films with Hydrogen Gas
Ye-Sul Jeong, Hyun-Uk Lee, Kyun Ahn, Je-Hoon Jeon, Se-Young Jeong and Chae-Ryong Cho Department of Nano Fusion Technology, Pusan National University, Miryang 627-706
Won-Jae Lee Department of Nano Engineering, Dongeui University, Busan 614-714
(Received 17 February 2008) Al-doped zinc oxide (AZO) thin lms were grown on glass substrates by radio-frequency (rf) magnetron sputtering at 250 C. The surface of the AZO lms was treated with hydrogen gas by using an atmospheric plasma (AP) system. The resistivity of the hydrogen-plasma treated lms was improved by approximately 40 % compared with that of the untreated lm. However, the crystal structure of the lms was unchanged by the plasma treatment. The optical transmission of the AZO lms was 80 % in the visible range and the band gap of the AZO lm treated with a hydrogen plasma was higher than that of the untreated AZO lm. The chemical bonding states of oxygen, aluminum and zinc elements in the AZO lms were examined by using X-ray photoelectron spectroscopy (XPS). XPS showed a decrease in the metallic Zn content of the AZO lms and an increase in the bonds with oxide functional groups, such as Al-O and Zn-O, in the lms after the hydrogen plasma treatment. PACS numbers: 73.61.Ga, 82.33.Xj, 78.20.-e, 68.55.-a Keywords: Al-doped ZnO, Atmospheric plasma, Hydrogen, Surface modi cation
bient. It treats the samples at atmosphere pressure and room temperature. Therefore, it can be applied to exible device processes. In this study, an atmospheric cold plasma system with hydrogen gas was used to examine the e ect of plasma treatment on the surface of AZO thin lms. In addition, the structural, the electrical and the optical properties, as well as the surface chemical bonding states, of the AZO lms were studied for various treatment times.
I. INTRODUCTION
Transparent conducting oxide (TCO) thin lms play a fundamental role in photovoltaic technology. Among them, materials such as tin oxide (SnO2), indium tin oxide (ITO) and zinc oxide (ZnO) have been studied and applied as electrodes in thin- lm solar cells [1{4]. Aldoped ZnO (AZO) lms are particularly interesting on account of their valuable properties, such as higher thermal stability and good resistance against damage by hydrogen plasma, compared with ITO [5]. However, a high temperature process or substrate bias control is required due to the AZO lms formation characteristics, where Al prevents ZnO grain growth. Therefore, in order to improve the quality of the lm surface, a rapid thermal annealing (RTA) process is normally used for the postdeposition annealing of AZO thin lms in a gas ambient and a vacuum. A hydrogen plasma treatment in a vacuum is reported to create n-type point defects, such as Zn interstitials or O vacancies, or a defect complex contributing free electrons to the ZnO lattice [6]. An atmospheric cold plasma (ACP) treatment does not require a high temperature annealing process and a vacuum am-
II. EXPERIMENTS AND DISCUSSION
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The AZO thin lms were prepared by RF-magnetron sputtering with a 2 wt.% Al2O3-doped ZnO ceramic target made from high-purity ZnO (99.99 % purity) and Al2O3 (99.99 % purity) powders. Corning 1737 glass was used as the substrate and the substrate-to-target distance was xed to 85 mm. TheAZO lms were deposited on glass substrates at 250 C with a RF power of 100 W. The base pressure in the chamber was
