Gas sensitivity of ZnO/La₂CuO₄ heterocontacts

The sensitivity to CO and H₂ of heterocontacts between p-type La₂CuO₄ and n-type ZnO semiconductors, and of the single oxides, as a comparison, is reported. Heterocontacts are prepared by mechanically pressing sintered pellets of the two oxides. Current-vontage (I-V) characteristics for the heterocontacts, measured in air at temperatures ranging from 25 to 400 °C, show typical p-n diode behaviour, while I-V curves for the single oxides are linear, showing ohmic behaviour. An increase in current, which is bias dependent for the heterocontacts, is observed in correspondence to variations of CO and H₂ concentrations. The I-V curves in the presence of reducing gases continue to show rectifying characteristics. The single oxides show little gas sensitivity and slow response times. Heterocontacts show no selectivity to CO, but higher sensitivity to gases than do CuO/ZnO contacts. The highest sensitivities are observed at 400 °C. The response time to H₂ is very fast (less than 1 min), while the response time to CO is much slower.