STATIC SPACE-CHARGE IN EVAPORATED ZNS-MN ALTERNATING-CURRENT THIN-FILM ELECTROLUMINESCENT DEVICES

The operation of alternating-current thin-film electroluminescent (ACT FEL) devices may be strongly affected by the presence of dynamic or st atic positive space charge within the phosphor layer during device ope ration. Dynamic space charge is a positive charge in the phosphor laye r which is periodically created and annihilated during each period of the applied voltage waveform. In contrast, static space charge is a po sitive 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 i s estimated to be similar to 7 x 10(16) cm(-3) 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 similar to 2.2 MV/cm and a clamping interface trap depth of simila r to 1.5 eV. Furthermore, from transferred charge trends as a function of the phosphor thickness it is concluded that the static space charg e in evaporated ZnS:Mn ACTFEL devices arises from metastable hole trap ping in the phosphor. (C) 1998 American institute of Physics.