Influence of carbon monoxide, water and oxygen on high temperature catalytic metal-oxide-silicon carbide structures

High temperature sensors, Schottky diodes and capacitors, based on catalytic metal-oxide-silicon carbide devices are investigated. Reducing gases like hydrogen and other hydrogen containing gases, decrease the barrier height and the flat band voltage, respectively, which is used as the sensor signal. The sensitivity of the devices at 600 degrees C to mixtures of carbon monoxide and oxygen with and without water vapour is studied in this paper. A large binary response of the sensors to carbon monoxide similar to the sensor response to hydrogen gas is observed. Close to the stoichiometric ratio of carbon monoxide and oxygen, the signal changes from a high to a low value corresponding to an excess of carbon monoxide and an excess of oxygen, respectively. When hydrogen is added to a mixture of carbon monoxide and oxygen, the signal changes from a high to a low value at a higher oxygen concentration. Since the response of these devices to hydrogen and hydrogen containing gases is supposed to emanate from hydrogen atoms, the mechanism of the response to carbon monoxide is discussed. The signal to carbon monoxide as well as to hydrogen decreases in the presence of water vapour and the reason for this is discussed. (C) 1997 Elsevier Science S.A. All rights reserved.