Luminescence and device application of GaN and AgGaS_2 doped with rare-earth impurities

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Preparation and photoluminescence measurements have been carried out on the GaN phosphor powder, sputtered GaN thin films and AgGaS_2 single crystals doped with rare-earth (RE) impurities.GaN : RE phosphor powders have been prepared by sintering of the GaN powder mixed with the rare-earth nitride which is either EuN or TbN. As a result, intense green and red emissions are observed for GaN : Tb and GaN : Eu, respectively. It has been concluded that the emissions are due to the emission of trivalent rare-earth impurities which is not purely the substitutional RE ion at the Ga site in the GaN lattice. They may be related to RE oxides or RE-oxygen impurity complex. Eu-doped GaN powder has also been prepared by the nitrization of the Ga_2S_3 doped with Eu. Emission from the substitutional Eu^3+ impurity has been observed for this powder sample. However, the emission intensity is very weak. Zn doping in GaN powder was successfully by the nitrization of the Ga_2S_3 : Zn. Thus, it is concluded … More that the doping of ER impurity into GaN under the thermal equilibrium condition is very difficult. A new method was also performed by the chemical reaction using Ga(NO_3)_3 and Eu(NO_3)_3 as starting materials for the preparation of GaN : Eu.Thin GaN films doped with RE (Eu and Tb) were grown on sapphire substrate by the RF magnetron sputtering. Red emission due to Eu^<3+> (620 nm) was observed for GaN : Eu films. Emissions were studied with relation to the growth conditions (substrate temperature, growth time and doping concentration) and annealing condition (annealing in NH^3). By optimizing these conditions, GaN : Eu films emitting red intense emission have been prepared. However for the GaN : Tb film, no Tb^<3+>-related emission has been observed.AgGaS_2 crystals doped with RE have been prepared by (1) sintering method, (2) melt-growth method and (3) iodine chemical vapor transport method. AgGaS_2 : Eu exhibited intense green emission at 2.3 eV related to the 5d-4f transition in Eu^<2+>. For the AgGaS^2 : Er, series of emission lines has been observed at about 2.3 and 1.9 eV. No infrared emission (1.5 μm) has been observed. Energies and number of the emission peaks are different depending on the preparation method. Since RE impurities are considered to be substitutionally occupy the Ag site, stoichiometry control and charge compensation in AgGaS^2 : ER are future subject. Less