Roles of shape and size of component crystals in semiconductor gas sensors: II. Response to N O2 and H2

The theoretical approach established on the response of semiconductor gas sensors to oxygen was extended to the response to N O2 (oxidizing gas) or H2 and CO (reducing gases) in air. The former extension was carried out simply by replacing the reduced adsorptive strength of oxygen by that of N O2. The resulting equations were found to well explain the N O2 sensing behavior of the devices using granular or lamellar crystals of W O3. The latter extension was carried out through a steady-state method; that is, the steady concentration of adsorbed oxygen (O-) was combined with the electronic equilibrium of the constituent crystals underneath to formulate the sensor response as a function of the partial pressure of each reducing gas. It was confirmed that the theory could account for the grain size effects and doping effect reported for Sn O2 -based devices fairly well.