EFFECT OF NO2 IN AIR ON THE ELECTRICAL CONDUCTANCE OF IN2O3 FILMS WITH AND WITHOUT ADDED ZNO PREPARED BY RF-SPUTTERING

The conductance of indium oxide films with and without added zinc oxide consisting of ultrafine particles with a mean particle size of ≤30 nm, decreased by a factor of about 500 upon changing from air to 10 p.p.m. NO2 in air at 150° C. The dramatic decrease in the conduction caused by NO2 adsorption is mainly attributed to the increase in the activation energy, E, in the Arrhenius relationship G=Goexp (-E/kT), while the pre-exponential factor, Go, is almost constant. The conductance measured in air and NO2 /air for the films with and without added zinc oxide can be fitted to this relationship in the temperature range below 250° C. The decrease in the carrier concentration is considered as the origin of the decrease in conductance caused by NO2 adsorption. The alternative explanation in terms of an increase in the grain-boundary potential, i.e. the mobility gap, can be ruled out because the depletion layer width is larger than the mean particle size. © 1990 Chapman and Hall Ltd.