Metal oxide semiconductors with highly concentrated oxygen vacancies for gas sensing materials: A review

[Display omitted] •Effects of oxygen vacancies on the properties of MOS are summarized.•Methods for introducing oxygen vacancies are summarized.•Applications of high oxygen vacancies materials in gas sensors are listed. The introduction of oxygen vacancies into metal oxide semiconductors is an effective way to enhance their gas sensing performance. In this review paper, firstly, the roles of oxygen vacancies on band structure, electrical conductivity, optical absorption and gas adsorption are presented. The presence of highly concentrated oxygen vacancies narrows the bandgap width of semiconductors, thus reducing the energy required for electron transition. It also increases the active sites on the material surface and enhances the chemisorption, thus improving the adsorption performance of the material. In addition, it also improves the electrical conductivity and light absorption ability of the material. Then, this review paper briefly introduced the state of the art of metal oxide semiconductors with highly concentrated oxygen vacancies fabricated by various processes, which are mainly divided into direct and indirect methods. At last, the application of metal oxide semiconductors with highly concentrated oxygen vacancies in the field of gas sensors is reviewed.