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

To investigate systematically the causes of the aging of thin film electrol uminescent devices, time-dependent current-voltage characteristics of doubl y doped ZnS:Pr, Ce, Mn layer has been investigated under a direct current h igh field as one of the accelerated aging methods. The surface roughness al ong 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 fo r current fluctuations during the measurement. It was observed that the lea kage current level after long-term stressing increased or decreased dependi ng on post-treatment indicating that the bulk-controlled conduction was the dominant mechanism determining long-term behavior and this mechanism is no t sensitive to the variations in the deposition parameters. The experimenta l results indicate the fact that the long-term conduction behavior of ZnS-b ased film may be related to defect redistribution after lowering barrier he ight during initial stressing. Finally, we suggest that an enhancement of c ontact adhesions via surface smoothing of the upper interface can contribut e to the long-term stability. (C) 1999 American Institute of Physics. [S002 1-8979(99)05713-8].