Effects of implantation conditions on the luminescence properties of Eu-doped GaN (original) (raw)
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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.
The photoluminescence/excitation (PL/E) spectroscopy of Eu-implanted GaN
Optical Materials, 2011
Several distinct luminescent centres form in GaN samples doped with Eu. One centre, Eu2, recently identified as the isolated, substitutional Eu impurity, Eu Ga , is dominant in ion-implanted samples annealed under very high pressures (1 GPa) of N 2. According to structural determinations, such samples exhibit an essentially complete removal of lattice damage caused by the implantation process. A second centre, Eu1, probably comprising Eu Ga in association with an intrinsic lattice defect, produces a more complex emission spectrum. In addition there are several unidentified features in the 5 D 0 to 7 F 2 spectral region near 620 nm. We can readily distinguish Eu1 and Eu2 by their excitation spectra, in particular through their different sensitivities to above-gap and below-gap excitation. The present study extends recent work on photoluminescence/excitation (PL/E) spectroscopy of Eu1 and Eu2 to arrive at an understanding of these mechanisms in terms of residual optically active defect concentrations. We also report further on the 'host-independent' excitation mechanism that is active in the case of a prominent minority centre. The relevance of this work to the operation of the red GaN:Eu light-emitting diode is discussed.
Luminescence properties of Eu-implanted GaN for full color micro light-emitting diode array
Journal of the Indian Institute of Science
Europium (Eu) was implanted into GaN epitaxial layer and its films were annealed at 0.1 atm NH 3 diluted with N 2 at a temperature range of 950−1100°C to remove any 'implantation damages'. Photoluminescence (PL) properties were measured in the temperature range 80−280 K by using He-Cd laser as an excitation source. Strong emission at 621 nm, corresponding to the transition from 5 D 0 to 7 F 2 states of Eu 3+ , was observed and the thermal quenching of the PL intensity was very small.
Photoluminescence and lattice location of Eu and Pr implanted GaN samples
Physica B: Condensed Matter, 2001
Rare earth (RE) ions implanted GaN films were studied by optical spectroscopy and RBS techniques. Sharp emission lines due to intra-4f n shell transitions can be observed even at room temperature for the Eu 3+ and Pr 3+ . The photoluminescence spectra recorded by the above band gap excitation reveal dominant transitions due to the 5 D 0 -7 F 1,2,3 lines at 6004, 6211 and 6632 ( A for the Eu 3+ and 3 P 0,1 -3 F 2,3 at 6450 and 6518 ( A, respectively, for the Pr 3+ . We report on the temperature dependence of the intra-ionic emissions as well as on the lattice site location of the RE detailed angular scans through the /0 0 0 1S and /1 0 % 1 1S axial directions; which indicates that for Pr, complete substitutionality on the Ga sites was achieved while for Eu a Ga displaced site was found. r
Effect of growth conditions on Eu3+ luminescence in GaN
Journal of Crystal Growth, 2010
Eu-doped GaN thin films were in situ grown on sapphire substrates by RF plasma-assisted solid-source molecular beam epitaxy technique. Strong red emission at $ 622 nm from 5 D 0 -7 F 2 radiative transitions in Eu 3 + ions was observed for all samples. The effects of important growth parameters, such as III/V ratio (Ga flux), Eu cell temperature (Eu flux) and growth temperature, on Eu 3 + photoluminescence were studied. X-ray diffraction and secondary ion mass spectroscopy measurements were performed to investigate thin film quality and Eu doping profiles. The strongest Eu 3 + luminescence was obtained from GaN:Eu thin films grown under slightly N-rich condition (III/V o 1), while the highest Eu 3 + emission efficiency was obtained in thin films grown under Ga-rich condition (III/V Z 1). The optimum Eu doping concentration for Eu 3 + luminescence is $ (0.1-1.0) at% for III/V r 1 ratio condition. Higher growth temperature ( 4 750 1C) was also found to enhance Eu 3 + luminescence intensity and efficiency.
Optical properties of high-temperature annealed Eu-implanted GaN
Optical Materials, 2006
A 10 nm thick epitaxially grown AlN cap has been used to protect the surface of a GaN epilayer both during Eu ion implantation and the subsequent high-temperature annealing. The 15 K photoluminescence (PL) intensity of the intra-4f Eu transition increases by two orders of magnitude when the annealing temperature is increased from 1000 to 1300°C. High-resolution PL spectra reveal that the emission lines due to the 5 D 0 -7 F 2 transition exhibit different dependencies on the annealing temperature in the studied annealing range. PL excitation measurements demonstrate band edge absorption by the GaN host at 356 nm, together with a broad excitation band centred at 385 nm. The PL spectra of the 5 D 0 -7 F 2 transition selectively excited by above band-gap absorption and by this broad excitation band are noticeably different. The first peak at 620.8 nm is suppressed when exciting below the GaN band gap. This demonstrates differing energy transfer processes for the different Eu luminescent peaks and is direct evidence for at least two kinds of different Eu sites in the host with distinct optical activation. Temperature dependent PL and PLE demonstrate that one of the two Eu-centres does not contribute to the room temperature luminescence.
2005
The emission properties of Eu doped GaN thin films prepared by interrupted growth epitaxy (IGE) were investigated through excitation-wavelength dependent and time-resolved photoluminescence (PL) studies. Under above-gap excitation (333-363 nm) large differences were observed in the Eu 3+ PL intensity and spectral features as a function of Ga shutter cycling time. The overall strongest red Eu 3+ PL intensity was obtained from a sample grown with a Gashutter cycling time of 20 minutes. The main Eu 3+ emission line originating from 5 D 0 ! 7 F 2 transition was composed of two peaks located at 620 nm and 622 nm, which varied in relative intensity depending on the growth conditions. The room-temperature emission lifetimes of the samples were non-exponential and varied from ~50 µs to ~200 µs (1/e lifetimes). Under resonant excitation at 471 nm ( 7 F 0 -> 5 D 2 ) all samples exhibited nearly identical PL spectra independent of Ga shutter cycling time. Moreover, the Eu 3+ PL intensities and lifetimes varied significantly less compared to above-gap excitation. The excitation wavelengths dependent PL results indicate the existence of different Eu 3+ centers in GaN: Eu, which can be controlled by the Ga shutter cycling time.
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.
Two colour experiments in Eu3+ implanted GaN
Journal of Alloys and Compounds, 2008
Two colour experiments can be used to study the excitation mechanisms of rare-earth ions in rare-earth doped wide-bandgap semiconductors as well as the quenching of their photoluminescence (PL). The combined excitation of Eu 3+ implanted GaN samples with a pulsed laser and a CW laser, corresponding, respectively, to a below bandgap excitation and to an above bandgap excitation, is investigated. A strong quenching of the rare-earth (RE) luminescence is observed with both lasers compared to the excitation with only one laser. The dependence of the Eu 3+ 5 D 0 lifetime quenching with the emission wavelength and excitation density of the CW laser is presented. The results are explained within the frame of a model describing the occurrence of an Auger effect between excited Eu ions and free carriers created by the CW laser.