Photo-induced charge (PIQ) and photo-induced luminescence (PIL) measurements are employed for the characterization of evaporated ZnS:Mn alternating-current thin-film-electroluminescent (ACTFEL) devices. PIQ and PIL measurements involve monitoring the charge and luminescence associated with the transport of UV-excited electrons or holes under the application of a constant applied voltage. The experiment is accomplished using a short UV laser pulse to create carriers near the upper phosphor/insulator interface while maintaining a constant voltage across the ACTFEL device in order to set the phosphor field. By changing the polarity of the applied voltage pulse, either electron or hole transport may be studied. PIL thresholds indicate that the critical field for electron-initiated electroluminescence in ZnS is ~1.04 MV/cm. PIQ trends indicate that electron transport is significantly more efficient than hole transport due to hole trapping in the ZnS. Hole trapping is characterized by a drift length of ~180 ± 70 nm, a hole lifetime of ~2 ps, and a capture cross-section of ~7 ´ 10–13 cm2. A capture cross-section of this magnitude corresponds to hole trapping by a negatively charged acceptor-like trap. It is speculated that this hole trap is a zinc vacancy complex.
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