THE ELECTRICAL-PROPERTIES OF LA2CUO4 ZNO HETEROCONTACTS AT DIFFERENT RELATIVE HUMIDITIES/

The humidity-sensing electrical properties of heterocontacts between p -type La2CuO4 and n-type ZnO semiconductors, and of the single oxides, as a comparison, were studied. The heterocontacts was prepared by mec hanically pressing sintered disks of the two oxides. The electrical ch aracterization of the heterocontacts was carried out using de and ac m easurements at various relative humidity (RH) values, in order to eval uate the sensing mechanisms and the electrical properties of these p-i l junctions. Their humidity sensitivity was explained in terms of the variation of the barrier height at the p-n junctions, due to the satur ation of the original interface states by physisorbed water, which lea ds to the release of trapped electrons, resulting in an increase in th e forward current. The higher the number of interface states, the high er the RH-sensitivity of the heterocontacts. Electrochemical impedance spectroscopy (EIS) measurements showed, at 90% RH, a distribution of capacitances with different relaxation times, which may be caused by t he electrolysis of water molecules at p-n junction sites. For their us e as humidity sensors, they showed a response of 4 orders of magnitude in the whole RH range tested, and a fast response time, The response of the heterocontacts was bias-dependent, tunable by externally applie d electric field. They also have stand-by capability and a self-cleani ng mechanism, which allow them to be described as intelligent material s.