AC-IMPEDANCE ANALYSIS OF GAS-SENSING PROPERTY IN CUO ZNO HETEROCONTACTS/

The a.c. impedances of a CuO(Na)/ZnO heterocontact have been investiga ted under a d.c. bias voltage (-10 to +10 V) in CO- and H-2-containing atmospheres at 250 degrees C. The reactance (imaginary component of t he impedance) shows characteristic changes depending on the gas specie s, measuring frequency and applied d.c. bias. By tuning the measuring frequency under a d.c. bias of -1 to -3 V, CO sensitivities higher tha n that obtained by d.c. measurements and high CO selectivity are obtai ned. The reactance changes are related to changes in both the resistan ce and capacitance components of the interface impedance. The product of the interface resistance and capacitance is found to be an effectiv e index for the evaluation of gas selectivity in heterocontact-type ga s sensors.