A high field electroluminescent device having two light emitting mechanisms—direct impact excitation and carrier recombination—was fabricated in order to improve the luminous efficiency. For the carrier recombination process, a TPD/Alq3 stacked layer and a ZnTe/ZnO stacked layer were used. Although the emission intensity from carrier recombination is poor, emission due to carrier recombination and impact excitation was observed from a single device. In this device, an electron has two roles: one is impact excitation and the other is recombination with a hole. It is shown that one electron gives two or more photons from a DC electroluminescent device.

In order to reduce the driving voltage of DC electroluminescent (EL) devices, an electron injection structure with a hydrogenated amorphous Si (a-Si:H) interlayer between a Ta2O5 layer and ZnS:Mn layer was investigated. It was shown that junction capacitance existed between the Ta2O5 layer and ZnS:Mn layer and that the junction capacitance decreased due to the insertion of the a-Si:H layer. These results were confirmed by impedance spectra. The threshold voltage decreased with the insertion of the a-Si:H layer, and luminance gradually increased over the threshold voltage compared with that in conventional DC-EL devices, because the interlayer formed a stepwise band structure in the device. Moreover, the carrier multiplication effect of a-Si was confirmed under photoexcitation. Although a clear multiplication effect was not obtained, the possibility of further efficiency improvement by the multiplication effect was shown.

To improve the efficiency of a DC Electroluminescent (DC-EL) device, we investigated the reduction of the driving voltage while maintaining the stability of the DC-EL device in this study. Mechanisms for both the current control and hot-electron generation under low voltage were embedded in the device. Usage of a p-Cu2O thick film with high-performance electrical properties for the formation of two semiconductive band barriers in series achieved these functions. The n-ZnO/p-Cu2O controlled current, and the p-Cu2O/n-ZnS:Mn generated hot electrons. The electrical characteristics of each junction demonstrated those of the p–n junction, and the driving voltage was divided into both the junctions. 98% of the driving voltage was applied to the hot-electron generation junction. Electroluminescence was obtained at approximately 20 V, because the local electric field at the junction accelerated electrons. Although the luminance was insufficient, it has been inferred that such a device structure is effective in decreasing driving voltage.