Long-term conduction behavior of white-light emitting ZnS-based phosphor films

Abstract

To investigate systematically the causes of the aging of thin film electroluminescent devices, time-dependent current-voltage characteristics of doubly doped ZnS:Pr, Ce, Mn layer has been investigated under a direct current high field as one of the accelerated aging methods. The surface roughness along to the direction perpendicular to the indium-tin-oxide-glass substrate and the high peak-to-valley roughness are assumed to be the main sources for current fluctuations during the measurement. It was observed that the leakage current level after long-term stressing increased or decreased depending on post-treatment indicating that the bulk-controlled conduction was the dominant mechanism determining long-term behavior and this mechanism is not sensitive to the variations in the deposition parameters. The experimental results indicate the fact that the long-term conduction behavior of ZnS-based film may be related to defect redistribution after lowering barrier height during initial stressing. Finally, we suggest that an enhancement of contact adhesions via surface smoothing of the upper interface can contribute to the long-term stability. (C) 1999 American Institute of Physics. [S0021-8979(99)05713-8].