Effects of amorphous Si on DC electroluminescent devices

Abstract

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.

Low-voltage DC electroluminescent device using semiconductive band barriers with Cu2O

“…The current is limited to less than 1.2 mA in the voltage range below 1 V. This current range agrees with the drive current of the conventional DC-EL device. 15,16) Therefore, the role of current control can be expected also in the DC-EL device with p-Cu 2 O. The current linearly increases with a large forward-bias voltage due to the resistance of Cu 2 O sheet.…”

“…The emission threshold voltage is approximately 20 V, which is less than half that of conventional DC-EL devices. 15,16) The average electric field of the emission layer was calculated from V 3 , divided by the film thickness, to confirm whether the hot electrons were generated in the local electric field of the junction. V 3 (98% of V 1 ) was divided into ZnS:Mn and CeO 2, because the resistance of p-Cu 2 O is low.…”

“…In terms of efficiency, we have investigated DC driving inorganic EL (DC-EL) devices. [13][14][15][16] However, DC driving severely limits the device structure. [17][18][19][20][21][22][23][24][25] In AC driving EL devices, hot electrons are transferred between the insulating layers; in a DC-EL device, it is necessary to inject electrons continuously from one side of an emission layer while maintaining a high electric field.…”