A comparison of conductance behaviour between SnO 2 and CdS gas-sensitive films

Abstract

The conductance behaviours of SnO 2 and CdS semiconducting films as a function of temperature and after rapid changes in temperature and in oxygen partial pressure are compared. Experimental results are given at different partial pressure of oxygen in dry mixtures with nitrogen in the temperature ranges 350–850 K for SnO 2 and 300–550 K for CdS. In the case of conductance response to rapid changes in oxygen partial pressure, results are given for both an increase and a decrease of the partial pressure. Some results are also given for SnO 2 films doped with aluminium and antimony. SnO 2 samples are in the form of thick films, which together with gold electrodes are screen printed on an alumina substrate. Spray pyrolysis is used for the deposition of CdS thin films from CdCl 2 and (NH 2) 2CS solutions on glass substrates. A similar sigmoidal variation of conductance during heating is found for both SnO 2 and CdS films with a shift of 200 K and more in the temperature scale for this variation between the two films. The results are discussed in the light of conduction models where the surface barriers at intergranular contacts dominate the film resistance.