HUMIDITY SENSITIVE ELECTRICAL-PROPERTIES OF DENSE ZNO WITH NONOHMIC ELECTRODE

The humidity sensitive electrical properties of ZnO dense sintered com pacts with two, one, or no ohmic contact are reported. Sintered ZnO di scs were prepared by traditional ceramic processing. Ohmic contacts we re obtained with Al electrodes. Non-ohmic contacts were made by mechan ically pressing Au sheets on the uncoated sides of sintered discs. Dar k current-voltage (I-V) characteristics of ZnO pellets were measured a t different relative humidity (rh) values and at room temperature. The I-V curves for pellets with one ohmic contact showed a diode behaviou r, with a rectifying character, attributed to the presence of a Schott ky barrier. The rectifying characteristics of ZnO pellets were enhance d in the presence of humidity, and the rh-sensitivity was bias-depende nt. The rh-sensitivity of dense ZnO pellets with a Schottky barrier ca n be related to the variation of the barrier height due to the presenc e of surface states. Their behaviour resembles that of p-n junctions, with a sensing mechanism which is different from those already propose d in the literature for ceramic materials.