Influence of the electrode materials on the electrical response of Zno-based contact sensors

The sensitivity to CO and H2 of heterocontacts between p-type La2CuO4 and n-type ZnO semiconducting oxides, and the humidity sensitivity of heterocontacts have been studied. Heterocontacts were prepared by mechanically pressing sintered pellets of the two oxides, or sintered pellets of ZnO and Au sheets. As ohmic electrodes, three different materials were applied on ZnO pellets (Zncontaining Ag, In- and Ga-containing Ag, and Al pastes). This paper reports the influence of the electrodematerials used as ohmic contact for ZnO on the chemical sensitive electricalresponse of both systems. For ZnO pellets with two ohmic electrodes, different resistivities were observed using the various electrodematerials. Current-voltage (I-V) characteristics for single ZnO pellets were linear, showing ohmic behaviour. Little chemical sensitivities were observed for ZnO pellets. I-V curves for heterocontacts showed a rectifying character, due to a p-n diode behaviour for contacts, and to a Schottky barrier behaviour for . For both systems, the rectifying character was enhanced in the presence of reducing gases (CO and H2) or humidity, respectively. The chemical response of the heterocontacts, which was due to the and interfaces, was dependent on the electrodematerials applied on ZnO pellets, with the same trend for both systems. The greater the resistivity of the ZnO pellets, the larger the sensitivity of the heterocontacts. Slight differences in the potential barrier heights are induced by the different resistivities of the three electrodematerials. The larger the band-bending at or type semiconducting oxide interfaces, the larger the influence of adsorbates, resulting in increased sensitivity.