The dependences of electroluminescent characteristics of ZnS:Mn thin films upon their device parameters

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Abstract
The dependences of brightness, emission efficiency η, average electric field EA, conduction current JA, and emission lifetime τ upon the device parameters such as film thickness, substrate temperature during evaporation, and Mn concentration have been systematically investigated in ZnS:Mn thin-film electroluminescent devices. The value of η increases rapidly with film thicknesses below 3000 Å but EA decreases slowly. These results can be explained by the increase of the crystallinity of the ZnS:Mn films. The value of η increases with the Mn concentration and reaches its maximum at about 0.45 wt %. At above this Mn concentration, η and τ decrease rapidly, EA increases, and JA decreases slowly. These results may be attributed to a decrease of hot electron energy and/or an increase of the nonradiative transition probability of the excited Mn centers. The brightness-voltage (B-V) hysteresis characteristic is observed in this Mn concentration region. This memory effect is also discussed.