Observation and simulation of space-charge effects and hysteresis in ZnS:Mn ac thin-film electroluminescent devices

We have shown from basic considerations that the negative resistance effect measured in thin-film electroluminescent devices must involve some variation of space charge in the phosphor layer. Time-delayed voltage pulse experiments indicate that positive space charge decreases spontaneously. By introducing the presence of deep donor levels which can be ionized by accelerated electrons and, when positively charged, have some typical decay time for the release of a hole, we have created a numerical model which is able to simulate negative resistance, time-delayed pulse experiments and the influence of temperature and frequency on the hysteretic behavior.