Theoretical approach to the rate of response of semiconductor gas sensor

The rate of response of a semiconductor gas sensor to a change in the partial pressure of O2, H2 or NO2 has been successfully formulated theoretically under the assumptions of volume depletion and a specific scheme of electron transfer (modified model). In each case, the rate is expressed as a logarithmic function of reduced resistance and its rate constant (reciprocal of time constant) is given by a combination of three terms, which reflect the rate of surface reactions, the donor density and the size of constituent crystals, respectively. Especially remarkable is the last term which leads to strong attenuations of the rate of response for the crystals with reduced size (n) exceeding 5 (spheres) or 3 (plates).