Band structure and high-field electron transport of a ZnS phosphor in AC thin-film electroluminescent devices

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 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. We have also examined how the band structure affects the high-field electron transport in ZnS.