On the excitation efficiency in ZnS:Mn thin-film electroluminescent devices

Abstract

In ac-coupled ZnS:Mn thin-film electroluminescent devices, the excitation efficiency ηexc depends on the insulator/ZnS interfaces and the excitation level. For optimized devices which are used in industrial production, ηexc does not depend on the transferred charge as long as the excitation level is below the saturation range. In the saturation range, ηexc decreases with increasing charge transfer. Hence the decrease of the total efficiency η at high excitation levels is partly due to the behavior of the excitation efficiency and not entirely to the decrease of the radiative efficiency ηlum. In devices with shallow insulator/ZnS interface states, however, charge injection starts at lower fields and ηexc increases strongly with the transferred charge and the applied voltage.

Chemical Vapor Deposition of ZnS:Mn for Thin-Film Electroluminescent Display Applications

“…Above this range, performance is degraded due to a nonradiative energy transfer process between Mn ions and defects. 35,36 In addition, the threshold voltage did not exhibit any dependence on Mn dopant levels, indicating that the low Mn dopant levels did not affect the dielectric properties of ZnS:Mn films or the value of threshold clamping field in the phosphor layer.…”

Laser annealing of thin film electroluminescent devices deposited at a high rate using high target utilization sputtering

“…A dramatic improvement is observed, which is possibly due to localized diffusion of the dopant ions and relaxation of the host lattice resulting in enhanced luminescent properties. However, this technique cannot be applied to temperaturesensitive substrate materials and it is also seen to have a detrimental effect on the L-V characteristics if a complete EL device is thermally annealed [9]. Whilst annealing is beneficial in terms of the luminescent properties of the ZnS:Mn thin film, any concomitant annealing of the interface region between the phosphor and the dielectric layers results in a modification of the electron emission properties, typically resulting in a softening of the L-V characteristics.…”

“…Post-deposition thermal annealing of EL devices has been shown to decrease the threshold voltage with increasing anneal temperature or anneal time [9,[18][19][20][21]. The softening of the luminance characteristic with thermal annealing has been attributed to a broad distribution of interface states [19].…”

“…The softening of the luminance characteristic with thermal annealing has been attributed to a broad distribution of interface states [19]. Thermal annealing of the phosphor layer prior to the deposition of the top dielectric layer has been observed to lead to asymmetric luminance characteristics due to the different thermal histories of the bottom and top interfaces [20]. The threshold voltage is lower when electron injection occurs at the top interface compared to the bottom and this difference increases with annealing temperature [20].…”

“…Thermal annealing of the phosphor layer prior to the deposition of the top dielectric layer has been observed to lead to asymmetric luminance characteristics due to the different thermal histories of the bottom and top interfaces [20]. The threshold voltage is lower when electron injection occurs at the top interface compared to the bottom and this difference increases with annealing temperature [20]. This difference was attributed to the creation of shallow traps at the top interface during annealing.…”