Thin film ZnS:Mn AC-electroluminescent device with a Ge layer

A new thin film electroluminescent device (indium tin oxide ITO-Y2O3- (ZnS:Mn)- Ge-Y2O3- Al) (type II) has been prepared, and is compared to the conventional structure (ITO- Y2O3- (ZnS:Mn) - Y2O3- Al) (type I). The optically active conduction charge is measured for both types in order to ascertain the effect of the Ge layer which is believed to act as a carrier injection source. We found that in this new structure, compared to type I, the amount of the conduction charge is larger, but the maximum luminance value is lowered by a factor of 2 to 3 and the breakdown voltage is slightly lowered. These results can be explained from the experimental observation that remarkable assymmetry of luminescence waveforms is present in the type II device, i.e., the Ge layer influences the electric field near the ZnS-Ge interface. The appearance of the type II display is improved compared to type I.