Low-voltage thin-film electroluminescent devices with low-resistivity stacked insulators

The characteristics and mechanism of low-voltage-driven thin-film electroluminescent (TFEL) devices with low-resistivity (10(6)-10(7)-ohms cm) SiO(2)/Ta(2)O(5) and Al(2)O(3)/Ta(2)O(5) stacked insulating films have been studied. At 50-Hz sinusoidal wave voltage excitation, the threshold voltage of devices with a ZnS:Mn emitting layer is below 40 V, and the brightness and luminous efficiency are above 1000 cd/m(2) and 4 lm/W, respectively, with 60 V voltage. The characteristics of brightness versus voltage (B-V) curves, integrated charge versus voltage (Q-V) figures, and luminous efficiency versus voltage (eta-V) characteristics are different from conventional devices. The study of a special semiconductor layer--a thin probe-doped layer located at a different part of the pure ZnS layer--has proved that the excitation efficiency is not homogeneous across the emitting layer in this kind of device, and its value decreases from the anode toward the cathode, which is opposite of that made with TFEL devices with high-resistivity insulators. By offering a model of space-charge-limited current, the mechanism of low-voltage-driven thin-film electroluminescence, its optoelectronic characteristics, and the distribution characteristics of excitation efficiency across the emitting layer can be thoroughly explained.