LOW-VOLTAGE THIN-FILM ELECTROLUMINESCENT DEVICES WITH LOW-RESISTIVITYSTACKED INSULATORS

The characteristics and mechanism of low-voltage-driven thin-film elec troluminescent (TFEL) devices with low-resistivity (10(6)-10(7)-Ohm cm ) SiO2/Ta2O5 and Al2O3/Ta2O5 stacked insulating films have been studie d. At 50-Hz sinusoidal wave voltage excitation, the threshold voltage of devices with a ZnS:Mn emitting layer is below 40 V, and the brightn ess and luminous efficiency are above 1000 cd/m(2) and 4 lm/W, respect ively, with 60 V voltage. The characteristics of brightness versus vol tage (B-V) curves, integrated charge versus voltage (Q-V) figures, and luminous efficiency versus voltage (eta-V) characteristics are differ ent from conventional devices. The study of a special semiconductor la yer-a thin probe-doped layer located at a different part of the pure Z nS layer-has proved that the excitation efficiency is not homogeneous across the emitting layer in this kind of device, and its value decrea ses from the anode toward the cathode, which is opposite of that made with TFEL devices with high-resistivity insulators. By offering a mode l of space-charge-limited current, the mechanism of low-voltage-driven thin-film electroluminescence, its optoelectronic characteristics, an d the distribution characteristics of excitation efficiency across the emitting layer can be thoroughly explained. (C) 1997 Optical Society of America.