Fabrication and Properties of ZnO Thin Films Prepared by Micro Channel Mist Mehtod
Toshiyuki KAWAHARAMURA, Hiroyuki NISHINAKA, Keisuke KAMETANI, Yoshio MASUDA, Masataka TANIGAKI and Shizuo FUJITA
Abstract:The fine channel mist (FCM) method has been developed, as a safe and economical growth technology of zinc oxide (ZnO) thin films. This technique utilized aqueous solution of zinc acetate, which is a safe material, as a zinc source, and this solution is supplied to the growth as a form of micro-sized mist by applying ultrasonic-power with the carrier gas of nitrogen. ZnO thin film was grown in an open system, where the mist of zinc acetate reacted with oxygen or water on a glass substrate at the temperature of 270 to 500 Ž. One of the key technologies was to flow the reactant gases in a micro-channel on the substrate. This allowed effective growth of ZnO by gcondensingh the flow to the substrate neighborhood and by rapidly improving of the collision probability of the source gases, resulting in the high efficiency (as high as 10 %) for the zinc source to form ZnO. The ZnO thin film hence grown was transparent with the naked eyes, that is, the optical transmission was higher than 90 % in the visible light region. Photoluminescence spectra exhibited near-band edge emission around 3.3 eV (375 nm) at room temperature, with weak deep level emission around 2.5 eV. The surface morphology changed in terms of growth conditions, reflecting different crystallographic properties. The physical properties of the films were obtained through this method as follows. The thickness, the electrical conductivity, and the growth rate were 50-5000 nm, 1-5 ƒ‹ám, and 1-200 nm/min respectively. The overall properties of ZnO thin films grown here suggested the potential of this novel growth technology being utilized to fabricate a transparent conducting film, ultraviolet absorber, and so on. Key Words:ZnO, Zinc acetate, Ultrasonic formation of mist, Fine-channel mist method, Micro-channel, Mist CVD, Transparent conductive thin films, Optical and electrical properties