Roles of Shape and Size of Component Crystals in Semiconductor Gas Sensors

The theoretical approach established on the response of semiconductor gas sensors to oxygen was extended to the response to (oxidizing gas) or and CO (reducing gases) in air. The former extension was carried out simply by replacing the reduced adsorptive strength of oxygen by that of . The resulting equations were found to well explain the sensing behavior of the devices using granular or lamellar crystals of . The latter extension was carried out through a steady-state method; that is, the steady concentration of adsorbed oxygen 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 -based devices fairly well.