Transferred charge analysis of evaporated ZnS:Mn alternating-current thin-film electroluminescent devices

Evaporated ZnS:Mn alternating-current thin-film electroluminescent ~ACTFEL! devices are assessed via frequencyand temperature-dependent transferred charge analysis. The frequency-dependent trends involve the threshold voltage and the slope of the transferred charge immediately above threshold, both of which increase with increasing frequency. At ;15–20 V above threshold, the slope of the transferred charge curve is relatively independent of frequency and is approximately equal to the physical insulator capacitance. The temperature-dependent trends indicate that the phosphor capacitance increases and the slope of the transferred charge immediately above threshold decreases with increasing temperature. These frequencyand temperaturedependent trends are interpreted as arising from metastable hole trapping in which holes created in the phosphor by band-to-band impact ionization remain trapped in metastable traps at the cathode interface instead of being annihilated by electrons trapped at interface states. © 1997 American Institute of Physics. @S0021-8979~97!08001-8#