Effect of growth conditions on Eu3+ luminescence in GaN (original) (raw)
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Japanese Journal of Applied Physics, 2011
The growth mode of europium (Eu)-doped GaN epitaxial films grown on a GaN template by rf plasma-assisted molecular beam epitaxy (PAMBE) was investigated with different III/V ratios under a constant Eu beam equivalent pressure ratio [P Eu =ðP Eu þ P Ga Þ]. The reflection high-energy electron diffraction (RHEED) patterns and atomic force microscopy (AFM) images revealed the transition of the growth mode from threedimensional (3D) to step-flow/two-dimensional (2D) by increasing the III/V ratio. When the films were grown in the 3D growth mode, Eu concentrations estimated by Rutherford backscattering spectrometry/channeling (RBS/channeling) were almost constant, although the III/V ratios varied. However, when the growth mode was transferred from 3D to step-flow/2D, precipitates on the surface abruptly increased while the Eu concentration abruptly decreased, indicating the abrupt degradation of Eu-incorporation in the film. Luminescence sites of Eu 3þ were sensitive to the III/V ratio, and Eu atoms have different luminescence sites in both growth modes. Furthermore, luminescence efficiency abruptly increased when the growth mode was transferred from 3D to step-flow/2D.
Effects of implantation conditions on the luminescence properties of Eu-doped GaN
Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions With Materials and Atoms, 2003
Europium (Eu) ions were implanted into gallium nitride (GaN) epitaxial layers with doses ranging from 1 Â 10 13 to 8 Â 10 15 cm À2 at room temperature (RT) to investigate the effects of implantation condition on the photoluminescence (PL) properties. The strong red emission peak from 4f-4f electron transition of Eu 3þ is observed at 621 nm after annealing at 1050°C for 30 min in 33% NH 3 diluted with N 2. The PL peak intensity at RT is almost the same as those from the near-band-edge emission of GaN. The PL intensity increases with increasing Eu dose up to 3 Â 10 14 cm À2 , but saturates around 1 Â 10 15 cm À2. At doses above 1 Â 10 15 cm À2 , the PL intensity decreases with increasing Eu concentration. The reasons for the decrease in PL intensity can be interpreted in terms of the concentration quenching due to high Eu concentration as well as residual damage created by implantation.
Photoluminescence studies of rare earth (Er, Eu, Tm) in situ doped GaN
Materials Science and Engineering: B, 2003
The emission properties of rare earth (RE)-doped GaN are of significant current interest for applications in full color displays, white lighting technology, and optical communications. We are currently investigating the photoluminescence (PL) properties of RE (Er, Eu, Tm)-doped GaN thin-films prepared by solid-source molecular beam epitaxy. The most intense visible PL under above-gap excitation is observed from GaN:Eu (red: 622 nm) followed by GaN:Er (green: 537 nm, 558 nm), and then GaN:Tm (blue: 479 nm). In this paper, we present spectroscopic results on the Ga-flux dependence of the Er 3+ PL properties from GaN:Er and we report on the identification of different Eu 3+ centers in GaN:Eu through high-resolution PL excitation (PLE) studies. In addition, we observed an enhancement of the blue Tm 3+ PL from AlGaN:Tm compared to GaN:Tm. Intense blue PL from Tm 3+ ions was also obtained from AlN:Tm under below-gap pumping.
Study of GaN:Eu[sup 3+] Thin Films Deposited by Metallorganic Vapor-Phase Epitaxy
Journal of The Electrochemical Society, 2008
Using metallorganic vapor-phase epitaxy, thin films of gallium nitride activated by Eu 3+ ͑GaN:Eu 3+ ͒ have been deposited on sapphire substrates at atmospheric pressure. Luminescence from Eu 3+ ions in GaN has been investigated using photoluminescence ͑PL͒ and PL excitation spectroscopy. Experimental results show that Eu 3+ ions are excited via energy transfer from the host. Analyses of the observed emission and excitation spectra indicate occupancy of multiple sites in the nitride lattice. Using a pulsed laser source, variation of emission intensity with increasing excitation intensity has also been examined. The possibility of emission saturation at high excitation intensity is discussed from the perspective of application in light-emitting diode sources.
Effect of optical excitation energy on the red luminescence of Eu 3+ in GaN
Photoluminescence ͑PL͒ excitation spectroscopy mapped the photoexcitation wavelength dependence of the red luminescence ͑ 5 D 0 → 7 F 2 ͒ from GaN:Eu. Time-resolved PL measurements revealed that for excitation at the GaN bound exciton energy, the decay transients are almost temperature insensitive between 86 K and 300 K, indicating an efficient energy transfer process. However, for excitation energies above or below the GaN bound exciton energy, the decaying luminescence indicates excitation wavelength-and temperature-dependent energy transfer influenced by intrinsic and Eu 3+ -related defects.
Photoluminescence studies of Eu-implanted GaN epilayers
physica status solidi (b), 2005
Photoluminescence (PL) of Eu-implanted GaN epilayers grown by Metalorganic Vapour Phase Epitaxy (MOVPE) was studied as a function of temperature. The implantation was done at ion energies of 75 keV, 200 keV and 350 keV with doses of 10 14 cm -2 and 10 15 cm -2 . PL spectra of all samples show the emission line assigned to the 5 D 0 -7 F 2 transition of Eu 3+ in GaN to be split into three spectral components at 620.7 nm, 621.6 nm and 622.5 nm. The split lines are seen to have very different temperature dependences of integrated intensity. Such splitting might be explained by Eu 3+ ion site multiplicity. The variation of the temperature quenching factor of the PL integrated intensity from sample to sample and from line to line suggests that optically active Eu 3+ ions are coupled to defects and impurities, thus forming complexes with different energy position of the carrier trapping level in the bandgap of GaN. The appearance and quenching of an additional PL line at 617.3 nm with increasing temperature is observed in the range of 13 -295 K.
Spectral and time-resolved photoluminescence studies of Eu-doped GaN
Applied Physics Letters, 2003
We report on spectral and time-resolved photoluminescence ͑PL͒ studies performed on Eu-doped GaN prepared by solid-source molecular-beam epitaxy. Using above-gap excitation, the integrated PL intensity of the main Eu 3ϩ line at 622.3 nm ( 5 D 0 → 7 F 2 transition͒ decreased by nearly 90% between 14 K and room temperature. Using below-gap excitation, the integrated intensity of this line decreased by only ϳ50% for the same temperature range. In addition, the Eu 3ϩ PL spectrum and decay dynamics changed significantly compared to above-gap excitation. These results suggest the existence of different Eu 3ϩ centers with distinct optical properties. Photoluminescence excitation measurements revealed resonant intra-4 f absorption lines of Eu 3ϩ ions, as well as a broad excitation band centered at ϳ400 nm. This broad excitation band overlaps higher lying intra-4 f Eu 3ϩ energy levels, providing an efficient pathway for carrier-mediated excitation of Eu 3ϩ ions in GaN.
Luminescence characteristics of Er-doped GaN semiconductor thin films
Journal of Alloys and Compounds, 2000
Semiconductors doped with rare earth atoms have been studied for more than a decade because of the potential of using them to 31 develop compact and efficient electroluminescence (EL) devices. Trivalent erbium ions (Er) are of special interest because they exhibit atomic-like transitions centered at 1540 nm, which corresponds to the low-loss window of silica-based optical fibers. While EL devices, based on Er-doped Si and GaAs materials, have been fabricated, their efficiency remains too low for practical applications. Several years ago an important observation was made that there was less detrimental temperature quenching of Er luminescence intensity for larger bandgap host materials. Therefore, Er-doping of wide gap semiconductors, such as the III-V nitrides, appears to be a promising approach to overcoming the thermal quenching of Er luminescence found in Si and GaAs. In particular, GaN epilayers doped with Er ions have shown a highly reduced thermal quenching of the intensity of the Er luminescence from cryogenic to elevated temperatures. The remarkable thermal stability of the light emission may be due to the large energy bandgap of the material, as well as to the optical inactivity of the material defects in the GaN films. In this paper, recent data concerning the luminescence characteristics of Er-doped GaN thin films are presented. Two different methods have been used for Er-doping of the GaN films: ion implantation and in situ doping 31 during epitaxial growth. Both methods have proven successful for incorporation and optical activation of Er ions. Infrared photoluminescence spectra, centered at 1540 nm, have been measured for various Er-doped III-N films. Considerably different emission spectra, with different thermal quenching characteristics, have been observed, depending upon the wavelength of the optical pump and the Er-doping method. Defect-related absorption centers permit excitation of the Er ions using below-bandgap optical sources. Elemental impurities, such as O and C, in the thin films have also been shown to influence the emission spectra and to lead to different optical characteristics.