Dependence of structural, electrical, and optical properties of ZnO:Al films on substrate temperature
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Z.L. Pei Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China, 110015
X. Wang Ion Beam Laboratory, Shanghai Institute of Metallurgy, Chinese Academy of Sciences, Shanghai, China, 200050
C. Sun and L.S. Wen Institute of Metal Research, Chinese Academy of Sciences, Shanghai, China, 110015 (Received 13 November 2000; accepted 17 April 2001)
ZnO:Al (ZAO) films were deposited on fused silica substrates heated to 350 °C by dc magnetron reactive sputtering from a Zn target mixed with 1.5 wt% Al. Films deposited on a substrate heated to a temperature between room temperature and 300 °C were (001)-oriented crystals, but those grown at 350 °C consisted of crystallites with (001) and (101) orientations. The dependence of electrical properties such as resistivity, carrier concentration, and Hall mobility on temperature was measured. The results indicate that the carrier concentration and Hall mobility increase with increasing temperature up to 250 °C, though the Al content remains unchanged in this temperature range. The probable mechanisms are discussed. The minimum resistivity of ZAO films is 4.23 × 10−4 ⍀ cm, with a carrier concentration of 9.21 × 1020 cm−3 and a Hall mobility of 16.0 cm2 v−1 s−1. The films show a visible transmittance of above 80%.
I. INTRODUCTION
Transparent conductive oxide films (TCO) that are both transparent in the visible region and electrically conducting have extensive applications in optoelectronic devices, including energy-efficient windows, burglar alarms, and window heaters, as well as electrodes for solar cells and especially for flat panel displays, such as liquid crystal displays, plasma display panels, field emission displays, organic electroluminescent devices, etc. The greatly increasing use of transparent conducting films for solid-state display devices especially in flat panel display devices has promoted the development of inexpensive materials such as ZnO and tin oxide (SnO2), in place of indium tin oxide (ITO). From the viewpoint that the film should be easily etched in order to form fine electrodes, ZnO films are more desirable than a)
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J. Mater. Res., Vol. 16, No. 7, Jul 2001 Downloaded: 12 Mar 2015
SnO2 films. However, the electrical properties of pure ZnO films are unstable at high temperature. Some dopants such as Al, Si, In, and Ga1–3 have been added in order to improve the electrical properties of ZnO films. Among them, Al-doped ZnO (ZAO) films show good electrical and optical properties. Furthermore, they offer a number of advantages including: (i) cheap and abundant raw materials; (ii) nontoxicity; (iii) tailoring of the ultraviolet absorption because the fundamental band gap of ZnO lies just at the end of the visible spectrum; (iv) good stability in a hydrogen plasma, which is of significance for applications related to amorphous silicon solar cells, etc.4,5 Generally, ZnO:Al (ZAO) films are fabricated by vacuum evaporation, chemical vapo
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