DC Electroluminescence on M-I-S Structures in Thin Films

Stable d.c. electroluminescence is observed in a cell with M-I-S structures in the form of thin films (Ta–Ta 2 O 5 –ZnS: TbF 3 –Au). To be able to observe d.c. electroluminescence in the cell, the Ta 2 O 5 insulating layer must be about 1000 Å–5000 Å thick and treated by heating in air at 250°C for about 10 minutes. Through such heat treatment, the d.c. conductance of the Ta 2 O 5 layer increases remarkably (about 10 3 times). The increase is due to the transition from an anomalous Poole-Frenkel effect to a normal one in the conduction process. This heat-treated Ta 2 O 5 layer plays an important role in the creation of hot electrons required to excite the electroluminescent cell.