Highly sensitive sensor for noxious gases using transparent conductive CuAlO2 thin film via molecular beam epitaxy

Abstract

Molecular beam epitaxy was used to prepare highly sensitive low-temperature sensors for noxious gases using p-type semiconductor CuAlO 2 thin films. Structural, morphological, and optical properties revealed that the CuAlO 2 films had a high-quality single-crystal structure with a rough surface and high transparency (>85%) in the visible-light–near-infrared (IR) band. Systematic investigations were carried out to examine the reduction gas sensing properties of the CuAlO 2 thin films for toxic and explosive gases such as CH 4 , H 2 S, CO, and NO. At 90 °C and at very low detection levels of 300 ppb, the CuAlO 2 films displayed excellent response to NO gas; the response time (17 s) and recovery time (68 s) were both very short. The CuAlO 2 sensor also showed excellent reproducibility. The NO gas sensitivity mechanism of the CuAlO 2 thin film was elucidated by comparing charge transport properties, which revealed that the enhanced gas sensing performance at the low concentration and the low operating temperature are attributed to the high-quality and conductivity of the film. Thus, CuAlO 2 thin films have considerable application potential for human health and environmental monitoring. • Highly sensitive low-temperature sensors for reducing noxious gases using p-type semiconductor CuAlO 2 thin film. • CuAlO 2 has high visible light transmittance which is comparable to that of the ITO (In 2 O 3 :Sn) film. • The CuAlO 2 film displayed satisfactory response to NO gas and short response and recovery time. • The NO gas sensitivity mechanism was elucidated by comparing charge transport properties.