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ZnO films which are doped with trivalent metals such as gallium and aluminum have been studied as transparent conductive films of displays, organic light-emitting devices and solar cells because they are highly conductive and less expensive than In2O3-SnO2 (ITO). ZnO films have been prepared by various techniques. Especially, metalorganic chemical vapor deposition (MOCVD) has the advantages as films can be deposited in large area at high growth rates. Generally used zinc precursors for MOCVD are diethyl zinc (DEZ) and bis[acetylacetonato]zinc (Zn(acac)2). Alkyl metals such as DEZ are highly volatile but react violently with air. Zn(acac)2, one of beta-diketonates, is stable against oxygen but both its vaporization and decomposition occur simultaneously in a source vessel because the vaporization temperature is close to the thermal decomposition temperature. Commonly used gallium and aluminum precursors are also alkyl metals and acetylacetonates. They have similar characteristics to the zinc precursors. In this study, trivalent metal doped ZnO thin films were prepared by a liquid-delivery MOCVD method using newly designed horizontal-typed vacuum chamber, where the precursor solutions with some beta-diketonates of zinc and gallium or aluminum were used. Isobutyrylpivaloylmethanato (IBPM) complexes of zinc and gallium resulted in higher deposition rate of 3-4 nm/min than the evaluated other beta-diketonates. The resistivity of 2-4 mol% Ga doped ZnO films prepared on glass substrate at 550oC were 2-5 x 10-3 ohm-cm. The transparency of about 100 nm-thick films was more than 85% in the visible range. Al doped ZnO films obtained in the same deposition conditions as Ga doped ZnO films were less conductive than the reported resistivity, the order of 10-4 ohm-cm. |