Photoluminescence and photoluminescence excitation studies of as-grown and P-implanted GaN: On the nature of yellow luminescence (original) (raw)
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Applied Physics Letters, 2000
We have studied the As doping effects on the optical characteristics of GaN films by time-integrated photoluminescence and time-resolved photoluminescence. When As is incorporated into the film, the localized defect levels and donor–acceptor pair transition become less resolved. The recombination lifetime of neutral-donor-bound exciton (I2) transition in undoped GaN increases with temperature as T1.5. However, the I2 recombination lifetime in As-doped GaN first decreases exponentially from 98 to 41 ps between 12 and 75 K, then increases gradually to 72 ps at 250 K. Such a difference is related to the isoelectronic As impurities in GaN, which generate nearby shallow levels that dominate the recombination process.
Luminescence Properties of As, P, and Bi as Isoelectronic Traps in GaN
MRS Proceedings, 1997
Photoluminescence spectra of high quality GaN epilayers, grown by MOCVD on sapphire substrates and implanted by isoelectronic ions: As, P, and Bi, were investigated. Post implant annealing was done at temperatures of up to 1150 °C, in a tube furnace under flowing NH 3 or N 2 , and in a rapid thermal annealing system in ambient of N 2 . The PL of GaN: P annealed at 1150 °C in NH 3 exhibited strong pair-type modulated structures on the short wavelength shoulder of an emission band.The band at 2.914 eV is due to the recombination of bound exciton to P-hole isoelectronic traps (P-BE), and the modulated structure results from electron-hole recombination at pairs of neutral donors and a hole on P isoelectronic traps. The PL of GaN: As, GaN: Bi showed an emission with peaks at 2.597 eV and 3.241 eV, due to the recombination of an exciton bond to As and Bi isoelectronic-hole traps. We also studied thermal quenching excitation spectra, and PL kinetics. The experimental results are discussed using a simple spherical potential-well model for isoelectronic traps: As, P, and Bi replacing nitrogen in GaN.
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.
Structural and optical properties of Gd implanted GaN with various crystallographic orientations
Thin Solid Films, 2017
Structure, morphology, and optical properties of Gd implanted GaN epitaxial layers were studied for (0001), (11 − 20), and (11 −22) orientations. The GaN layers grown by MOVPE on sapphire were subsequently implanted with 200 keV Gd + ions using fluences of 5 × 10 15 and 5 × 10 16 cm −2. Dopant depth profiling was accomplished by Rutherford Back-Scattering spectrometry (RBS). Structural and optical changes during subsequent annealing were characterized by RBS, Raman spectroscopy, and photoluminescence measurements. Post-implantation annealing induced a structural reorganization of GaN structure in the buried layer depending on the introduced disorder level, i.e. depending on the implantation fluence and on crystallographic orientation. The defect density depth distribution was evaluated by RBS. The surface morphology and optical properties depend on particular crystallographic orientation.
Intensity dependence of photoluminescence in GaN thin films
Applied Physics Letters, 1994
We report the intensity dependence of band-gap and midgap photoluminescence in GaN films grown by electron cyclotron resonance (ECR) microwave plasma-assisted molecular beam epitaxy. We find that the band-gap luminescence depends linearly while the midgap luminescence has a nonlinear dependence on the incident light intensity. These data were compared with a simple recombination model which assumes a density of recombination centers 2.2 eV below the conduction band edge. The concentration of these centers is higher in films grown at higher microwave power in the ECR plasma.
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.