The dependence of Europium (Eu)-related luminescence intensity on the Eu concentration in Eu-doped GaN was studied. This luminescence is observed at 622 nm and originates from the intra-4f transition of the Eu 3+ ion. The intensity of the luminescence increased with increasing Eu concentration, up to about 2 at. %, and then abruptly decreased. It was found that polycrystalline growth began to be induced at Eu concentrations of more than 2 at. %. In addition, clear evidence for the formation of EuN compounds was obtained by x-ray diffraction and extended x-ray absorption fine structure analysis. The cause of the concentration quenching is likely to be related to the polycrystalline growth as well as EuN formation.
Variation of the luminescence spectra of Eu-doped GaN with varying Eu concentration ranging from 0.6to8.0at.% was investigated. Eu-related luminescence originating from the D05-F27 transition of Eu3+ was observed at about 622nm. The luminescence basically consisted of three peaks. The relative intensity of the three peaks changed remarkably at the Eu concentration of around 2.0–3.5at.% which corresponds to a structural phase transition from a single crystalline to a polycrystalline structure. This indicates that the incorporation site of Eu in GaN is very sensitive to the structural properties of the GaN host material.
PACS 68.55.Ln, 71.20.Eh, 78.55.Cr Magnetic properties of Er-doped GaN and Tb-doped GaN films grown by molecular beam epitaxy (MBE) on sapphire substrates (0001) were studied. Magnetization measurements were carried out under magnetic fields ranging from -5 to 5 T, and both samples were reasonably interpreted to exhibit a predominant paramagnetic character. However, for Er-doped GaN, clear finite steps around zero fields were observed throughout the temperature range of 5 K to 300 K, suggesting the coexistence of ferromagnetic order.
A single crystalline Eu-doped GaN was grown by gas-source molecular beam epitaxy and photoluminescence (PL) properties were studied. The PL spectra show red-emission at 622 nm originating from intra 4f-4f transition of Eu 3C ion without band-edge emission of GaN. The peak shift of the red-emission with the temperature variation from 77 K to room temperature is less than 1.6 meV, and thermal quenching of the luminescence was found to be small compared with the band-to-band transition. Fourier transform infrared spectra showed an absorption peak at about 0.37 eV, which may be due to a deep defect level. The intensity of the red luminescence and the defect-related absorption peak increased with increasing Eu concentration, and a close correlation in the intensity was observed between them. These results suggest that the deep defect level plays an important role in the radiative transition of Eu 3C ion in GaN and the optical process for the luminescence at 622 nm was discussed with the relation to the defect. q
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