Damage accumulation and implanted Gd and Au position in a- and c-plane GaN
Introduction
Ion implantation doping of GaN has attracted increasing interest in the last decades due to its potential for the precise control of the distribution and concentration of dopants [[1], [2], [3], [4]]. It was found in the previous research that in rare earth doped GaN the lattice site occupied by dopant can significantly influence the luminescence properties of the doped layers in GaN [1]. The drawback of implantation is introduction of defects and damage which can deteriorate optical properties, thus the damage recovery after the annealing is real issue. Ion-beam channelling allows the identification an impurity site of relatively high concentration by direct comparison between matrix and impurity signals [1,4]. Dopant position is closely connected to damage accumulation in the implanted GaN lattice as vacancies and larger extended defects created during ion implantation directly influencing the dopant position in the modified crystalline matrix.
Rutherford Back-Scattering spectrometry in channelling mode (RBS/C) makes it possible to determine defect concentrations with depth resolution, dopant depth profiles and dopant position in a host crystalline matrix via angle scans of the backscattered ion yield close to the channelling axis. RBS/C has been applied in the past by many groups to investigate implantation damage build-up in GaN in various crystallographic orientations (e.g. [[5], [6], [7], [8]]), where dynamic annealing (the recombination of interstitials and vacancies) was identified as a main reason for radiation hardness of GaN which strongly depends on the implantation conditions (see e.g. [9,10]). Damage accumulation was studied in polar and non-polar GaN layers, but various dopant positions in different crystallographic orientations are still not fully explored. The lattice-site location of rare-earth ions in polar GaN (c-plane) (0001) was studied in [11,13] and Ga-substitutional site was found as a preferential. However, non-polar GaN (a-plane) (11–20) was not investigated in details from this point of view.
Lorenz et al. [8] have performed RBS/C experiments including angular scans in (0001) GaN implanted with 300 keV Eu ions at fluences of about 1015 cm−2 and subsequently annealed at 1000 °C and it was shown that Eu is located on substitutional lattice sites in a host matrix and annealing does not induce the further incorporation of Eu into substitutional sites. However, in this work was used RBS/C in the tilted 〈10−11〉 plane enabling evidence of a small displacement along the c-axis from near-substitutional Ga sites in GaN. Our intention is to use the similar procedure to follow the dopant position in crystalline host in details. A similar study performed in another associated semiconductor crystal, ZnO, at higher ion implantation fluences up to 1016 cm−2 has shown that from a certain damage limit, the annealing causes a massive decline in rare-earth dopant in substitutional positions; this analysis was done only for polar ZnO (0001) [7,13].
Implantation into various crystallographic orientations exhibits differences, which have been studied by several groups with the conclusion that defect accumulation is different for c-, a- and m-plane GaN [6,14] and the references therein. The work [6] has identified several defect-accumulation regimes for Ar 300-keV implantation in GaN and at ion implantation fluences ranging between 1 × 1015 and 4 × 1015 cm−2, where defect profiles exhibit distinct variation of the shape compared with those simulated by the Stopping and Range of Ions into Matter (SRIM) code.
A steepest increase in damage was observed for c-plane GaN [6]. The authors claim that beside primary defects, the influence of the Ar ions themselves cannot be excluded [6].
The crystallographic orientation used for implantation influences the optical response of the implanted structure and we have found such differences for various crystallographic orientations in other crystalline structures such as sapphire and lithium niobate (see [15,16]). The annealing procedure influences dynamic recovery and point-defect diffusion, possibly including large defect stabilisation, which are closely connected to the dopant lattice position and depend on the ion-implantation parameters. This issue is still important to study.
Comprehensive information on the dopant position after ion implantation into specific crystallographic orientations can be obtained using a combination of normal and non-normal ion channelling. Either the RBS channelling (RBS/C) procedure is used along the normal axis at a given GaN orientation (the axis is very close to the normal axis to the sample surface), or non-normal channelling can be implemented using additional axial channels at appropriate angles found based on higher crystal symmetry [17]. Non-normal channelling is mostly used for compressive or tensile strain determination from an angle shift of non-normal axes, but it can also be used for an angular scan to study the dopant position.
For the reasons mentioned above, we decided to conduct an experiment using Au and Gd ion implantation at 400 keV at ion fluences up to 5 × 1015 cm−2 to avoid complete amorphisation. Dopant positioning was done simultaneously using non-normal channelling to investigate the specific position in GaN and its modification after annealing. The structure modification and vacancies introduced by ion implantation were experimentally determined by angular scans with respect to normal and non-normal channelling directions and simulation of the angular scans was provided using FLUX [18]. Finally, the results were discussed in connection with photoluminescence properties.
Section snippets
GaN implantation and RBS channelling analysis
GaN layers with a thickness of 3 μm were grown by low-pressure Metal-Organic Vapour-Phase Epitaxy (MOVPE) on (0001) and (1−102) sapphire substrates. GaN layers were oriented along (0001) and (11–20) planes. The GaN layer deposition conditions are presented in recent works for (0001) [19] and for (11–20) [20]. GaN layers were implanted with Au+ and Gd+ ions using energy of 400 keV at fluences ranging from 1 × 1014 to 5 × 1015 cm−2. The implantation angle was 7° to prevent channelling. All
Au and Gd profile in RBS/C
The Au and Gd-dopant signals from RBS channelling spectra for c- and a-plane GaN in as-implanted and as-annealed samples are presented in Fig. 1. As we are concentrated on dopant behaviour and positioning, the whole RBS/C spectra are not presented and can be found in [22,23]. It is possible to notice the differences between the dopant signal in random and aligned directions for both GaN orientations and all ion-implantation fluences for Au implantation in Fig. 1a–d (the lowest ion fluence,
Discussion
It can be concluded that c-plane GaN for both implanted ion species shows more progressive surface-damage accumulation, higher thickness of the surface damage and higher deeper-damage accumulation than a-plane GaN. Furthermore, surface and deeper damage are more separated for lighter ion-implanted GaN, particularly in a-plane GaN:Gd. Strong surface-damage recovery is observed after the annealing mainly for low ion fluences and deeper damage is partially removed in c-plane GaN:Au, while it stays
Conclusions
We realized experiment, where the c- and a-plane GaN epitaxial layers were implanted with Au and Gd ions at energy of 400 keV using implantation fluences ranging from 5 × 1014 cm−2 to 5 × 1015 cm−2. An increase in ion-implantation fluence has caused a double-maximum profile of Au distribution, which can be correlated to the structural transformation at a certain ion-implantation fluence limit (in our case at 5 × 1015 cm−2 for Au ions), a bimodal depth profile connected to the preferential
Acknowledgement
The research has been carried out at the CANAM (Centre of Accelerators and NuclearAnalytical Methods) infrastructure LM 2015056. This publication has been supported by the OP RDE, MEYS, Czech Republic under the project CANAM OP, CZ.02.1.01/0.0/0.0/16_013/0001812, by the Czech Science Foundation (GACR No. 18-03346S).
References (42)
- et al.
Ion implantation into gallium nitride
Phys. Rep.
(2001) - et al.
Ion implantation into GaN
Mater. Sci. Eng.
(2001) - et al.
Implantation damage formation in a-, c- and m-plane GaN
Acta Mater.
(2017) - et al.
Lattice site location and optical activity of Er implanted ZnO
Nucl. Inst. Methods Phys. Res. B
(2003) - et al.
Comparative study of radiation damage in GaN and InGaN by 400 keV Au implantation
Nucl. Inst. Methods Phys. Res. B
(2004) - et al.
Lattice location and optical activation of rare earth implanted GaN
Mater. Sci. Eng. B
(2003) - et al.
A comparison of the structural changes and optical properties of LiNbO3, Al2O3 and ZnO after Er+ ion implantation
Nucl. Inst. Methods Phys. Res. B
(2014) - et al.
Structural and optical properties of Gd implanted GaN with various crystallographic orientations
Thin Solid Films
(2017) - et al.
The structural changes and optical properties of LiNbO3 after Er implantation using high ion fluencies
Nucl. Inst. Methods Phys. Res. B
(2014) - et al.
Erbium ion implantation into different crystallographic cuts of lithium niobate
Opt. Mater.
(2012)
50 years of ion channeling in materials science
Nucl. Inst. Methods Phys. Res. B
Computer-simulation of channeling in single-crystals
Nucl. Inst. Methods Phys. Res. B
Damage accumulation and structural modification in c-plane and a-plane GaN implanted with 400 keV Kr and Gd ions
Surf. Coat. Technol.
Molecular dynamics study of defect formation in GaN cascades
Nucl. Inst. Methods Phys. Res. B
A study of the structural properties of GaN implanted by various rare-earth ions
Nucl. Inst. Methods Phys. Res. B
A new iterative process for accurate analysis of displaced atoms from channelling Rutherford backscattering spectrometry
Nucl. Inst. Methods Phys. Res. B
Defect production in neutron irradiated GaN
Nucl. Inst. Methods Phys. Res. B
Lattice site location of optical centers in GaN:Eu light emitting diode material grown by organometallic vapor phase epitaxy
Appl. Phys. Lett.
Effect of ion species on the accumulation of ion-beam damage in GaN
Phys. Rev. B
Structural and optical characterization of Eu-implanted GaN
J. Phys. D. Appl. Phys.
Cited by (9)
Evolution of Au nanoparticles in c-plane GaN under the heavy ion implantation and their optical properties
2024, Journal of Alloys and CompoundsGradual modification of the YSZ structures by Au ion implantation and high-energy Si ion irradiation
2023, Ceramics InternationalCombined Au/Ag nanoparticle creation in ZnO nanopillars by ion implantation for optical response modulation and photocatalysis
2023, Applied Surface ScienceCitation Excerpt :Similar effect of compression in c-oriented facet of ZnO and contrary, expansion in a-plane facet have been observed in ZnO bulk irradiated samples as well in [23]. Implanted Au dopant preferably do not enter any substitutional position due to higher Au-ion radii [44], but rather is positioned in interstitial positions and create clusters. It is expectable that the ZnO will be modified preferably with heavier ions, however it is interesting, that dually Au, Ag-ion implanted samples exhibited the same or lesser structure modification even the sum of both ion fluences is equal or higher compared to the solely Au-ion implanted samples (see Fig. 4).
Multi-direction channelling study of the Ag:YSZ nanocomposites prepared by ion implantation
2021, VacuumCitation Excerpt :The deepening of the damage layer in the case of higher fluences can be connected to the higher defect diffusion into the underlying non-implanted region and to the swelling of the implanted layer caused by defect accumulation. This anisotropy of implantation damage for irradiation in various crystallographic orientations has been discussed for several crystals such as ZnO [39,40], YSZ [18,35] and LiNbO3 [41]. In the RBS-C measurements, the maximum of the disorder level is the lowest for the (110)-oriented YSZ, where also the deformation release is observed at higher implantation fluences than in (100) and (111)-YSZ orientations.
Ion Implantation into Nonconventional GaN Structures
2022, Physics (Switzerland)Energetic Au ion beam implantation of ZnO nanopillars for optical response modulation
2022, Journal of Physics D: Applied Physics