The Detection of Carbon Monoxide by the Oxide-Semiconductor Hetero-Contacts

Abstract

The hetero-contacts of CuO/ZnO and NiO/ZnO are prepared by mechanically pressing both sintered pellets and the gas sensing characteristics of these hetero-contacts are investi-gated. When reducing gases were fed to the hetero-contact, the current across the interface increased in all cases (Fig.1). Very high sensitivity and selectivity for CO gas were observed by CuO/ZnO contact at 260°C under the applied voltage of +0.5 V (Fig.3). The gas sensitivity and selectivity were controlled by changing the applied voltage in both CuO/ZnO and NiO/ZnO (Figs.4, 6). The decrease in the contact potential (Table 1) and the increase in the capacitance at the junction (Figs.7-9) by the reducing gases were observed in these hetero-contacts. In addition, the current was increased by not only the reducing gases without oxygen in the carrier gas but also incombustible gas (CO2) (Fig.10). It is assumed from these experimental results that the increase in the cu rrent by the reducing gases is due to 1) the decrease in the potential barrier height at the junction by the desorption of chemisorbed oxygen or 2) the formation of a new channel for the current which flows through the interface states made of adsorbed molecules on the p-type semiconductor (Fig.11).