Development of Blue-Emitting EL devices with High Color-Purity and Brightness

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This research aims at the development of blue-emitting electroluminescence(EL)devices with high color-purity and brightness based on Tm-doped ZnS grown by metalorganic molecular beam deposition (MOMBD). The results of the study are summarized below.1. Tn-doped ZnS films have been successfully grown on GaAs and glass substrates by MOMBD, for the first time, using diethylzinc and diethyl sulfide or hydrogen sulfide as Zn and S sources and elemental Tm as the dopant.2. The grown films have shown blue photoluminescence which is ascribed to the f-f transitions within Tm^<3+> ions. The transition processes in Tm^<3+> inos were investigated and compared with the results of film and powder samples. Photoluminescence a13EA\ : nd electroluminescence measurements have indicated that the dominant excitation process of Tm^<3+> ions would be not a direct excitation by hot electrons but an indirect excitation by energy transfer from the ZnS matrix.3. The light-emitting layr with Tm-modulation-doped structures for EL devices have been designed for improving the efficiencies of blue emission and excitation. The parameters of the structure have been optimized the basis of the result described i13EA\ : n section 2.4. ZnS : Tm layrs consisting of delta-doped layrs have been grown by MOMBD.It has been found that the luminescence properties depend on the doping parameters, e.g., sheet concentration of delta-doped Tm and distance between the adjacent sheets. How13EA\ : ever, secondary ion mass spectroscopy measurements have shown that depth profile of delta-doped layrs was not abrupt enough for the present purpose. The observed concentration broadening is yet to be investigated in detail for further improvement i13EA\ : n the abruptness.