Atomistic understanding of semiconductor gas sensors

Oxide semiconductors form a group of compounds whose specific properties of surfaces and interfaces are used for gas sensing. Our fundamental understanding of the operation principles of these devices is still insufficient. The abundance of phenomena on open oxide–semiconductor surfaces at elevated operation temperatures of the sensors is a central reason for the situation, in addition of the effects originating in the electrode–semiconductor contacts. The exchange of lattice oxygen with the surrounding atmosphere and a possible diffusion of oxygen through oxygen–vacancy donors in n-type oxides, especially at elevated temperatures, have also strong effects on the behaviour of semiconductor gas sensors. Atomistic understanding of surfaces is the basis for the understanding of both the receptor and transducer functions of semiconductor gas sensors. The rutile structure tin dioxide, SnO2, together with its most stable (110) face is the example material here. Especially, we consider the oxygen chemistry at the SnO2 (110) surface together with its connection to dipole layers and band-gap surface states. For example, the role of tin (II) ions at the reduced SnO2 (110) surface is discussed. A “transistor model” is also given to describe the transducing properties of semiconductor gas sensors.