Characteristics of pulse excited electroluminescence from ZnS films containing rare earth fluroide

The transient behavior of the electrical and the optical properties under pulse excitation has been studied and analyzed in detail on the electroluminescent devices made of Au-ZnS: NdF3- Ta2O5-Ta composite films. The ZnS-Ta2O5interface is capable of accommodating a large number of trapped electrons, up to 10¹³cm^-2, with the majority of the interfacial states located at a fixed energy below the conduction band of ZnS. Carrier injection is achieved by electrons tunneling through the Au-ZnS Schottky barrier at a field of 2.6×10⁶V/cm. The threshold field of impact excitation for 1 percent NdF3in ZnS was found to be 1.5×10⁶V/cm; while the coefficient of impact excitation at 2.6×10⁶V/cm was estimated to be 1750 cm^-1. In addition, the emission time constants of several rare earth fluorides were also studied.