Abstract
Abstract. The carbon monoxide (CO) gas sensing properties of low-resistance heavily Ga-doped ZnO thin films were evaluated. The ZnO films with a thickness of 50 nm were deposited at 200 °C by ion plating. The electrical properties of the ZnO films were controlled by varying the oxygen assist gas flow rate during deposition. The CO gas sensitivity of ZnO films with Au electrodes was investigated in nitrogen gas at a temperature of 230 to 330 °C. CO gas concentration was varied in the range of 0.6–2.4% in nitrogen gas. Upon exposure to CO gas, the current flowing through the film was found to decrease. This response occurred even at the lowest temperature of 230 °C, and is thought to be the result of a mechanism different than the previously reported chemical reaction.
Highlights
ZnO is a substance for which various applications such as gas sensors and ultraviolet light sensors are anticipated
Under the same growth condition, these Ga-doped ZnO films were polycrystalline with a wurtzite-type hexagonal structure from a cross-section transmission electron microscopy (TEM) and in-plane X-ray diffraction (XRD) measurements (Yamada et al, 2007b)
The carrier concentration was ≥ 1.0 × 1020 cm−3 and, from the temperature dependence of the Hall-effect measurement for samples deposited under same conditions, it was found
Summary
ZnO is a substance for which various applications such as gas sensors and ultraviolet light sensors are anticipated. The response mechanism is understood to have involved chemical reactions between gas molecules and the ZnO surface. We carried out an evaluation of the sensitivity of these polycrystalline ZnO thin films to CO gas. During growth, flowing oxygen was used as an assist gas, with the flow rate being varied between 5–25 cm3 in order to control the structure and properties of the films.
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