A simple model for the hysteretic behavior of ZnS:Mn thin film electroluminescent devices

A model is proposed for the observed hysteretic behavior of ac-coupled ZnS thin-film electroluminescent devices. The following mechanisms are invoked: (1) tunnel injection from ZnS-dielectric interfaces (E4106 V/cm), (2) electron-hole pair generation, (3) deep trapping of holes, leading to space-charge formation, (4) charge storage at the ZnS-dielectric interfaces, and (5) direct recombination of injected electrons and trapped holes. When these mechanisms are combined in a self-consistent numerical simulation model, a bistability of charge transfer versus applied voltage is obtained which exhibits many of the characteristics of the observed device behavior. Experimental evidence in support of the individual assumptions is also discussed.