Hot-electron impact excitation of ZnS:Tb alternating-current thin-film electroluminescent devices

A new method of performing hot-electron impact excitation experiments using alternating-current thin-film electroluminescent (ACTFEL) devices is reported. This method relies on the use of a field-control circuit to control the magnitude of the phosphor field and consists of plotting the intensity of a given electroluminescence transition, normalized by the amount of conduction charge which flows while the field-control circuit is asserted (the electroluminescence intensity of a given transition divided by the conduction charge is denoted the impact excitation quantum yield ηie), as a function of the phosphor field Fp. ηie vs Fp is measured for ZnS:Tb ACTFEL devices fabricated by atomic layer epitaxy (ALE) and by sputtering. ηie exhibits a threshold at approximately 0.5 MV/cm and saturation at approximately 1.5 MV/cm. The magnitude of ηie for the ALE ACTFEL device depends strongly on temperature; in contrast, ηie for the sputtered ACTFEL device is virtually temperature independent.