Excitation efficiency in thin-film electroluminescent devices: Probe layer measurements

The study of the excitation efficiency ηexc on thin-film electroluminescent devices with special semiconductor layer—a very thin probe-doped layer located at different part of the pure ZnS layer—has proved that ηexc is not homogeneous across the active layer. Moreover, this variation of ηexc depends on the amount of the transferred charge. At high excitation range, ηexc decreases continuously from the cathode toward the anode of the active layer. This behavior of ηexc is related to a space charge located in some part of the ZnS layer and generated by the energetic electrons. This space charge reduces the total efficiency of a conventional device when operating at high excitation range.