Electrical Dependence of ZnS Thin Films Exposed to H 2 O

In order to study the humidity dependence of thin‐film ceramic‐substrate electroluminescent (EL) devices below the luminescence threshold, two devices were evaporated—one with a smaller average grain size in the active layer than the other. The devices were exposed to various levels of relative humidity and were electrically characterized using charge‐voltage (Q‐V) measurements. It was found that the presence of water in the active layer decreased its leakage resistance while it increased the capacitance. Water was found to leave the small grain film much faster than the large grain film when subjected to the same conditions. The changes observed in the active layers of both devices were not fully reversible, and it is postulated that a new phase, possibly ZnO , has grown on the surface of the ZnS grains.