High-Field Electron Transport of the ZnS Phosphor in AC Thin-Film Electroluminescent Devices

A full-band Monte Carlo simulation of the hot carrier distribution and impact excitation yield for ZnS doped with Mn⁺² and Tb⁺³ is performed. A nonlocal empirical pseudopotential calculation has been performed for ZnS and used in the full-band Monte Carlo model which includes all the pertinent electron scattering mechanisms. Band-to-band impact ionization and impact excitation of luminescence centers are included, both of which are threshold phenomena crucial to the operation of an AC thin-film electroluminescent (ACTFEL) device. The impact excitation yield (the number of excited centers per traversing electron in the phosphor) exhibits a monotonic increase with increasing phosphor field in agreement with experiment. However, at high fields where impact ionization begins to significantly affect the transport, the impact excitation yield is somewhat suppressed.