Effects of additives on semiconductor gas sensors

The effects of additives of various metals and metal oxides on SnO2 and ZnO sensors are examined. The gas sensitivity (k) usually goes through a maximum with increasing temperature, and the effects of additives can be approximately compared in terms of the temperatures (TM) at the maxium of gas sensitivity (kM). It is shown that TM is well correlated with the temperature at which the catalytic oxidation of the sample gas proceeds at a certain rate. The effects of additives on k seem to be more complex. Based on XPS measurements, two types of sensitization mechanism, chemical and electronic, are proposed.