7. II-VI Semiconductor-Based Thin Film Electric and Electronic Gas Sensors

This chapter describes II-VI semiconductor films that have been applied to sensing various gases and vapors. Their gas responses have been stimulated by heat or light, and their readouts are enabled by transducing elements that usually comprise resistive principles. Previous studies on gas-sensitive II-VI semiconductors have consistently shown that these materials must meet similar requirements to other gas-sensitive materials, such as metal oxides. These requirements include small grain size, high porosity, optimal charge carrier concentration, and high chemical surface activity. Hence, part of the research on II-VI semiconductors as gas-sensitive elements involves exploring methods and routes that allow tailoring the semiconductor’s morphology, structure, chemical, and electronic properties. Among various available synthetic routes for II-VI semiconductors, chemical bath, precipitation, or hydrothermal processes are the most popular methods, usually assisted by other secondary deposition methods to integrate the synthesized materials over the appropriate gas sensing transducing platforms. The integrated II-VI semiconducting compounds are generally in the form of thin or thick layers containing spherical-like particles or other low-dimensional or hierarchical structures in the form of flakes or dendrites. These low-dimensional or hierarchical structures typically report superior gas responses than traditional spherical-like particles. Here we discuss in detail the fabrication processes, synthetic routes, and gas sensing properties of II-VI semiconducting films. The discussion addresses the most common factors influencing II-VI semiconductors’ gas sensing properties, their possible gas sensing mechanism(s), and the metrics of their functionality.