CO Gas Identification by Use of Complex Impedance of pn Heterocontact Comprising of Na-Added CuO and ZnO

Abstract

To improve the gas selectivity for carbon monoxide from hydrogen, the complex impedance characteristics under DC bias voltages were studied on a pn semiconductor heterocontact comprised of 1mol%Na2O-added CuO (as a p-type semiconductor) and ZnO (as an n-type), in the atmosphere of air-balanced CO or H2 gas (concentration: 4000ppm) at 250 and 400°C. In this heterocontact system, the capacitance component of the equivalent-circuit at the interface at 250°C was larger in the CO mixture, but smaller in the H2 mixture than that in air. As the results of characteristic changes of the equivalent-circuit components to each ambient gas at 250°C, it was shown that CO gas was selectively distinguishable from H2 gas by using a decrease in the absolute value of reactance at 10kHz under the bias voltage of -1V. Moreover, the identification of CO and H2 gases was shown to be feasible by DC bias dependence of reactance at a fixed frequency and by frequency dependence of reactance at a fixed DC bias. The CO gas identification by use of Na-modified CuO/ZnO was found to be feasible at a lower temperature of 250°C than that for Na-free CuO/ZnO (at 400°C).