Selectivity mechanisms in resistive-type metal oxide heterostructural gas sensors

Resistive-type semiconducting metal oxide (SMOX) sensors offer exciting possibilities for designing sensing systems that can detect extremely low concentrations of gasses relevant for industrial applications, environmental monitoring, and human health and safety. Research on this technology has produced sensors with high response, but the ability to predictively design sensing systems for specific applications requires improvements in selective detection. Gas selectivity is necessary to differentiate between multiple gas species that may be present in a given application. This has prevented wide-spread use of this technology in real-world settings. In this work, studies on gas selectivity in semiconducting metal oxide sensors are reviewed with specific emphasis on heterojunctions and fundamental sensing mechanisms. Concepts relating both to receptive and transduction sensor mechanisms are explained. The effects due to gas surface interactions and electronic equilibration are compared and discussed. Both modeling efforts and experimental literature are presented to explain fundamental mechanisms that control sensor behavior. Sensor selectivity is examined to further both fundamental understanding as well as increase real-world applications of semiconducting metal oxides.