Photoluminescence X-ray Excitation Spectra in Eu-doped GaN Grown by Organometallic Vapor Phase Epitaxy
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Photoluminescence X-ray Excitation Spectra in Eu-doped GaN Grown by Organometallic Vapor Phase Epitaxy S. Emura1, K. Higashi1, A. Itadani2, H. Torigoe2, Y. Kuroda2, A. Nishikawa3, Y. Fujiwara3, and H. Asahi1 1
ISIR, Osaka University, 8-1, Mihoga-oka, Ibaraki, Osaka 567-0047, Japan
2
Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima, Kita-ku, Okayama 700-8530, Japan
3
Division of Materials and Manufacturing Science, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
ABSTRACT X-ray-excited luminescence of GaN doped with Eu ions as a luminescent center was observed in the wavelength range from 350 nm to 650 nm. Three peaks at 375 nm, 550 nm and 622 nm were found. To survey the mechanism of the photoluminescence due to non-resonance excitation, photoluminescence X-ray excitation spectra are also measured. The mechanism of the luminescence occurrence was briefly discussed based on the model developed by Emura et al. INTRODUCTION As well known, rare earth compounds and rare earth ions as the dopant in some matrices are of uniqueness in the magnetism and the luminescence natures. The uniqueness conducts to many practical devices. In such situation, there are still few examples that rare earth ions as dopant in a semiconductor were utilized for the effective devices. A GaN-based red light-emitting diode (LED) is expected to enable the fabrication of nitride-based monolithic optical devices for fullcolor displays and/or lighting technology. Recently, Fujiwara and co-workers successfully grew the Eu-doped GaN (GaN:Eu) by organometallic vapor phase epitaxy and reported the first demonstration of the current-injected red emission at room temperature using the GaN:Eu as an active layer of the LED structure [1]. For the improved performance of the LED device, understanding of the local structures around the optically active Eu3+ ions should be required. X-ray absorption fine structures (XAFS) method has several advantages. In particular, as the initial states of the electron transition by X-ray irradiation are deep core levels such as a 1s orbital for the rather light elements and a 2p orbital for heavy elements, element selective detection can be carried out. In this contribution, we try unique XAFS method in the secondary process detecting mode like fluorescence mode and total electron yield method to investigate the local structures around the optically active Eu3+ ions. In this method, we do not detect fluorescence X-rays, which is usually adopted for dilute systems, but catch the visible photoluminescence. Even if the several local surroundings around the dopant elements simultaneously exist in the matrix, this method has the potential to distinguish those, because the photoluminescence peak energy is sensitive about the local alignment of the dopant element.
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EXPERIMENT The GaN:Eu samples were prepared by organometallic vapor-phase epitaxy techniques. The group III and V sources were trimethylgallium, and trimethylaluminium and ammonia. Eu3+ ions were doped using tr
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