EFFECTS OF INTERFACE STATES ON GAS-SENSING PROPERTIES OF A CUO/ZNO THIN-FILM HETEROJUNCTION

Humidity- and gas (CO, H-2)-sensing properties of CuO/ZnO thin-film junctions fabricated by different procedures have been investigated. Junctions in which the lower layer surface is exposed to air before stacking the upper layer (type I) and junctions deposited continuously (type II) have been prepared by the sputtering method. The type II junction shows little sensitivity to humidity and flammable gas (CO and H-2) compared to the type I junction. The interface capacitance in type I is almost independent of the applied bias. This indicates that the interface states are dominant for determining the electrical properties of the junction. The interface states formed by exposure to air are suggested to play important roles in chemical sensing.