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 frequency- and 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 frequency- and temperature-dependent 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.