Growth optimisation of ZnS:Mn thin film phosphors for high intensity miniature electroluminescent displays

This paper details an investigation into the deposition by RF magnetron sputtering of thin film phosphors specifically for use in laterally emitting thin film electroluminescent (EL) devices. The work presented here is concerned with the use of co-sputtering to optimise luminous efficiency and the use of transient (decay time) measurements to quantify the luminescent quality of the films. Thin films of phosphor were deposited by radio frequency (RF) magnetron sputtering in a custom built four electrode cluster deposition system. 800 nm films of ZnS:Mn were simultaneously co-sputtered from ZnS and ZnS:Mn (1 wt.%) solid targets. The thin films were deposited at different manganese concentrations by varying the RF power applied to each target. The films were deposited directly onto 100 mm diameter (100) n-type silicon substrates, or onto a layer of 300 nm of Y2O3 to fabricate electroluminescent test devices. Luminescence was characterised via photoluminescent excitation using a 337 nm pulsed N2 laser, with the PL optimum obtained at 0.38 ZnS:Mn power ratio. Transient luminescent measurements confirm that the luminescent decay constant decreases with manganese concentration in the ZnS:Mn thin films and proves a direct correlation with the Mn dopant concentration. The correlated Mn concentration vs decay constant results are presented as a potential non-destructive (in situ) technique for characterising this phosphor during deposition.