The stability of transparent conducting Al‐ and Ga‐doped ZnO (AZO and GZO) thin films in a high humidity environment has been investigated for the purpose of finding substitutes for the indium‐tin‐oxide (ITO) thin films used in transparent electrode applications. It was found that the resistivity of polycrystalline AZO and GZO thin films prepared with a thickness in the range from 50 nm to 300 nm at a substrate temperature below 200 °C always increased when long‐term tests were conducted in air at a temperature of 60 °C and a relative humidity of 90%, whereas ITO thin films remained relatively stable in the same environment; however, AZO and GZO thin films with a thickness above approximately 200 nm were sufficiently moisture‐resistant. The resistivity stability of AZO and GZO thin films was considerably related to crystallinity factors such as crystallite size. In addition, the resistivity increase is attributed to carrier transport dominated by grain boundary scattering resulting from the trapping of free electrons due to oxygen adsorption on the grain boundary surface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transparent conducting indium-tin-oxide (ITO) thin films with a thickness in the range from approximately 15 to 450 nm are in practical use as transparent electrode in liquid crystal display (LCD) applications. However, because of the high cost and scarcity of indium, transparent conducting impurity-doped ZnO such as Al-and Ga-doped ZnO (AZO and GZO) has recently attracted much attention as a promising alternative material [1,2]. In addition to the cost advantage of AZO, zinc being abundant and nontoxic, AZO thin films prepared on glass substrates have recently been reported with a low resistivity on the order of 10 -5 Ω cm [3], which is comparable to the lowest resistivity obtainable for ITO thin films. On the other hand, the resistivity of polycrystalline doped ZnO thin films has been found to increase drastically when used in hightemperature oxidizing environments; the stability of resistivity was strongly dependent on the film deposition temperature [4][5][6]. Since the fabrication of LCDs frequently requires thin-film deposition at a temperature below approximately 200 °C [7,8], the resistivity stability of doped ZnO thin films prepared at low temperatures must be investigated in activated oxidizing environments such as an atmosphere with high relative humidity. In this paper, the stability of transparent conducting AZO and GZO thin films in a high humidity environment is investigated for the purpose of finding substitutes for ITO thin films used in transparent electrode applications.Transparent conducting AZO and GZO thin films were prepared on glass (OA-10, Nippon Electric Glass Co., Ltd.) at a substrate temperature below 200 °C by pulsed laser deposition (PLD), dc or rf magnetron sputtering (MSP) and vacuum arc plasma evaporation (VAPE) methods [9][10][11]. The as-deposited AZO and GZO films used in the stability tests were prepared with a thickness in the range from 20 to 200 nm at a substrate temperature in the range from 68 to 200 °C; the obtained resistivity is on the order of 10 -3 to 10 -4 Ω cm. For the purpose of comparing the stability, non-doped ZnO, non-doped In 2 O 3 and ITO thin films were also prepared in the same range of thicknesses and substrate temperatures as the doped ZnO films described above. The electrical properties described in the following were always measured in air at room temperature by the van der Pauw method.The resistivity of all non-doped and doped ZnO thin films prepared under the deposition conditions described above was found to increase with exposure time up to 1000 h in the high humidity environment (air at 90% relative humidity and 60 °C) tests; in contrast, all non-dopedThe resistivity of transparent conducting Al-and Ga-doped ZnO (AZO and GZO) thin films prepared with a thickness in the range from 20 to 200 nm on glass substrates at a temperature below 200 °C was found to increase with exposure time when tested in a high humidity environment (air at 90% relative humidity and 60 °C). The resistivity stability (resistivity increase) was considerably affected by the ...
Density of expanded fluid selenium was measured in the temperature and pressure ranges up to 1650°C and 700 bar including the liquid‐vapour critical point by the x‐ray absorption method. For the measurements, a new type of cell made of polycrystalline sapphire and a high‐pressure vessel of authors' own design were developed. The critical temperature, pressure and density of 1615 ± 5°C, 385 ± 5bar, 1.85 ± 0.03g cm−3, respectively, were obtained. We found that isochores bend in the semiconductor‐metal transition region. The shape of the isochore seems an elongated inverse‐S letter. The diameter of the liquid‐vapour coexistence curve is deviated from the law of the rectilinear diameter to the liquid side slightly around the SC‐M transition region and strongly near the critical point. A distinct crossover was also found in the critical exponent β; the value of β drastically changes from 0.30 to 0.10 when the critical point is approached.
A newly developed Al-doped ZnO (AZO) thin-film magnetron-sputtering deposition technique that decreases resistivity, improves resistivity distribution, and produces high-rate depositions has been demonstrated by dc magnetron-sputtering depositions that incorporate rf power (dc+rf-MS), either with or without the introduction of H2 gas into the deposition chamber. The dc+rf-MS preparations were carried out in a pure Ar or an Ar+H2 (0%–2%) gas atmosphere at a pressure of 0.4Pa by adding a rf component (13.56MHz) to a constant dc power of 80W. The deposition rate in a dc+rf-MS deposition incorporating a rf power of 150W was approximately 62nm∕min, an increase from the approximately 35nm∕min observed in dc magnetron sputtering with a dc power of 80W. A resistivity as low as 3×10−4Ωcm and an improved resistivity distribution could be obtained in AZO thin films deposited on substrates at a low temperature of 150°C by dc+rf-MS with the introduction of hydrogen gas with a content of 1.5%. This article describes the effects of adding a rf power component (i.e., dc+rf-MS deposition) as well as introducing H2 gas into dc magnetron-sputtering preparations of transparent conducting AZO thin films.
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