Evidence for Band-to-Band Impact Ionization in Evaporated ZnS:Mn Alternating-Current Thin-Film Electroluminescent Devices

摘要

Evidence is presented that the normal operation of evaporated ZnS:Mn alternatingcurrent thin film electroluminescent (ACTFEL) devices involves electron-hole pair generation by band to band impact ionization. Four observations are offered to support this assertion. These observations involve: (i) empirical field clamping trends, (ii) experimental and simulated trends in charge transfer characteristics, (iii) experimental attempts to assess the interface distribution using a field control circuit, and (iv) Monte Carlo simulation trends. Furthermore, the absence of overshoot in measured capacitance voltage and internal charge phosphor field curves indicates that a majority of the holes created by impact ionization are trapped at or near the phosphor/insulator interface. The multiplication factor (i.e., the total number of electrons transferred across the phosphor divided by the number of electrons injected from the phosphor/insulator cathode interface) is estimated, from device physics simulation of experimental trends, to be of the order 4-8 for evaporated ZnS:Mn ACTFEL devices operating under normal conditions.