Conductivity model for sputtered ZnO-thin film gas sensors

The electrical properties of reactively sputtered ZnO thin films used for chemical sensors are investigated in N-2 and oxidizing atmosphere by Hall measurements. The measured carrier concentration and mobility of the polycrystalline ZnO films are well described by combining compensated electron conduction within the crystallites and thermionic emission of carriers across the grain boundaries. Results of a computer simulation are given. It is shown that the increase of resistance in the presence of oxidizing atmospheres is owing to the reduction of the electron concentration whereas the mobility remains unchanged. The ZnO films are much more sensitive to oxidizing atmosphere than predicted by the simulation. This aspect is discussed in detail. (C) 1997 Elsevier Science S.A.