Static space charge in evaporated ZnS:Mn alternating-current thin-film electroluminescent devices

The operation of alternating-current thin-film electroluminescent ~ACTFEL! devices may be strongly affected by the presence of dynamic or static positive space charge within the phosphor layer during device operation. Dynamic space charge is a positive charge in the phosphor layer which is periodically created and annihilated during each period of the applied voltage waveform. In contrast, static space charge is a positive space charge in the phosphor layer whose charge state does not change appreciably during steady-state operation of the ACTFEL device. The static space charge density of evaporated ZnS:Mn ACTFEL devices is estimated to be ;7310 cm from measured trends in the phosphor clamping field as a function of phosphor thickness. This static space charge density estimate implies a cathode clamping field of ; 2.2 MV/cm and a clamping interface trap depth of ;1.5 eV. Furthermore, from transferred charge trends as a function of the phosphor thickness it is concluded that the static space charge in evaporated ZnS:Mn ACTFEL devices arises from metastable hole trapping in the phosphor. © 1998 American Institute of Physics. @S0021-8979~98!06902-3#