Lattice Location Studies Research Articles

Lattice Location Studies of the Amphoteric Nature of Implanted Mg in GaN

AbstractDespite the renewed interest in ion implantation doping of GaN, efficient electrical activation remains a challenge. The lattice location of 27Mg is investigated in GaN of different doping types as a function of implantation temperature and fluence at CERN's ISOLDE facility. The amphoteric nature of Mg is elucidated, i.e., the concurrent occupation of substitutional Ga and interstitial sites: following room temperature ultra‐low fluence (≈2 × 1010 cm−2) implantation, the interstitial fraction of Mg is highest (20–24%) in GaN pre‐doped with stable Mg during growth, and lowest (2–6%) in n‐GaN:Si, while undoped GaN shows an intermediate interstitial fraction of 10–12%. Both for p‐ and n‐GaN prolonged implantations cause interstitial 27Mg to approach the levels found for undoped GaN. Implanting above 400 °C progressively converts interstitial Mg to substitutional Ga sites due to the onset of Mg interstitial migration (estimated activation energy 1.5–2.3 eV) and combination with Ga vacancies. In all sample types, implantations above a fluence of 1014 cm−2 result in >95% substitutional Mg. Ion implantation is hence a very efficient method to introduce Mg into substitutional Ga sites, i.e., challenges toward high electrical activation of implanted Mg are not related to lack of substitutional incorporation.

Performance of resistive-charge position sensitive detectors for RBS/Channeling applications

The performance of two types of 1×1cm2 photodiode position sensitive detectors (PSDs) based on resistive charge division was evaluated for their use in Rutherford Backscattering/Channeling (RBS/C) experiments in blocking geometry. Their energy resolution was first determined for ~5.5MeV alpha particles from a radioactive sources, and values of full width half maximum (FWHM) of 22keV and 33keV were achieved using a shaping time constant of τ=2.0μs. Additional tests were performed using backscattered 4He particles from the 2.0MeV beam of a Van de Graaff accelerator. While the 22keV FWHM detector failed after exposure to less than 5×106cm−24He particles, the other did not show any noticeable deterioration due to radiation damage for a fluence of 4×108cm−2. For this type of PSD position resolution (τ=0.5μs) standard deviations of ΔL=0.072mm at ~5.5MeV and ΔL=0.247mm at 1.1MeV were achieved.RBS/Channeling experiments using PSD were performed on several crystalline samples, showing that this setup seems suitable for lattice location studies, particularly for heavy ions implantation (D≳1015at/cm2) on light substrates like Si, SiC, and AlN.

Lattice site location and luminescence studies of AlxGa1−xN alloys doped with thulium ions

Rare earth doped AlGaN is being considered for the development of new optoelectronic devices. This wide band gap compound provides lower thermal quenching of rare earth intra-4fn transitions making room temperature operation possible. In this work a detailed study of AlxGa1−xN (x=0.15, 0.77) samples grown by halide vapor phase epitaxy on (0001) sapphire implanted with Tm is presented. The samples were implanted at room temperature with 300keVTm ions to fluences of 1×1014cm−2 and 1×1015cm−2. The damage accumulation and the rare earth lattice site location are investigated by Rutherford Backscattering/Channeling Spectrometry. The structural measurements show a higher resistance of the lattice to irradiation damage with the increase of the AlN content. The analysis of angular scans along different axes using the Monte Carlo code FLUX allows the determination of the rare earth lattice sites. Results for Al0.15Ga0.85N show that Tm ions occupy two preferential sites: the high symmetry substitutional Ga/Al site and a site displaced by ∼0.3Å along the c-axis from this regular site.Rapid thermal annealing treatments at 1200°C under N2 ambient were performed to remove implantation damage and promote the optical activation of rare earth intra-4fn transitions. Photoluminescence measurements were performed to characterize the thulium ions spectroscopic transitions. The effects of thermal annealing and fluence on the fraction of rare earth optically active ions are exploited and discussed.

Lattice location and annealing studies of Hf implanted CaF2

Hafnium ions were implanted into calcium fluoride single crystals. The lattice damage introduced by the implantation was investigated with the Rutherford backscattering (RBS) channelling technique. The lattice location of the implanted ions was determined by performing channelling measurements for the 〈110〉 crystal direction. A comparison of the angular scan with Monte Carlo simulations leads to the conclusion that >90% of the Hf ions are on Ca sites directly after implantation. Subsequent annealing of the samples was performed in a rapid thermal annealing apparatus. Perturbed angular correlation (PAC) measurements with 181Hf(181Ta) show quadrupole interactions with νQ1=300(3) MHz (η=0.00), νQ2=1285(13) MHz (η=0.43) and νQ3=1035(10) MHz (η=0.00) after annealing up to 1200K.

Crystal field analysis ofPm3+(4f4)andSm3+(4f5)and lattice location studies ofNd147andPm147inw−AlN

We report a detailed crystal field analysis of ${\mathrm{Pm}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ as well as lattice location studies of $^{147}\mathrm{Pm}$ and $^{147}\mathrm{Nd}$ in 2H-aluminum nitride $(w\text{\ensuremath{-}}\mathrm{AlN})$. The isotopes of mass 147 were produced by nuclear fission and implanted at an energy of $60\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. The decay chain of interest in this work is $^{147}\mathrm{Nd}\ensuremath{\rightarrow}^{147}\mathrm{Pm}\ensuremath{\rightarrow}^{147}\mathrm{Sm}$ (stable). Lattice location studies applying the emission channeling technique were carried out using the ${\ensuremath{\beta}}^{\ensuremath{-}}$ particles and conversion electrons emitted in the radioactive decay of $^{147}\mathrm{Nd}\ensuremath{\rightarrow}^{147}\mathrm{Pm}$. The samples were investigated as implanted, and also they were investigated after annealing to temperatures of $873\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ as well as $1373\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The main fraction of about 60% of both $^{147}\mathrm{Pm}$ as well as $^{147}\mathrm{Nd}$ atoms was located on substitutional Al sites in the $\mathrm{AlN}$ lattice; the remainder of the ions were located randomly within the $\mathrm{AlN}$ lattice. Following radioactive decay of $^{147}\mathrm{Nd}$, the cathodoluminescence spectra of ${\mathrm{Pm}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ were obtained between $500\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and $1050\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ at sample temperatures between $12\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. High-resolution emission spectra, representing intra-4$f$ electron transitions, were analyzed to establish the crystal-field splitting of the energy levels of ${\mathrm{Sm}}^{3+}\phantom{\rule{0.3em}{0ex}}(4{f}^{5})$ and ${\mathrm{Pm}}^{3+}\phantom{\rule{0.3em}{0ex}}(4{f}^{4})$ in cationic sites having ${C}_{3v}$ symmetry in the $\mathrm{AlN}$ lattice. Using crystal-field splitting models, we obtained a rms deviation of $6\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ between 31 calculated-to-experimental energy (Stark) levels for ${\mathrm{Sm}}^{3+}$ in $\mathrm{AlN}$. The results are similar to those reported for ${\mathrm{Sm}}^{3+}$ implanted into $\mathrm{GaN}$. Using a set of crystal-field splitting parameters ${B}_{nm},$ for ${\mathrm{Pm}}^{3+}$ derived from the present ${\mathrm{Sm}}^{3+}$ analysis, we calculated the splitting for the $^{5}F_{1}$, $^{5}I_{4}$, and $^{5}I_{5}$ multiplet manifolds in ${\mathrm{Pm}}^{3+}$ and obtained good agreement between the calculated and the experimental Stark levels. Temperature-dependent lifetime measurements are also reported for the emitting levels $^{4}F_{5∕2}\phantom{\rule{0.3em}{0ex}}({\mathrm{Sm}}^{3+})$ and $^{5}F_{1}\phantom{\rule{0.3em}{0ex}}({\mathrm{Pm}}^{3+})$.

The unique role of ion beam analysis in modeling the thermal evolution of hydrogen in Si implanted at doses required for ion cutting

Hydrogen-ion implantation is capable of precise cutting of materials to remove a thin layer for transfer to alternate substrate. Combined with wafer bonding, this technique is capable of joining dissimilar materials to yield heterostructures such as silicon-on-insulator. This has spawned a renewed interest in the behavior of implanted hydrogen in Si. Rutherford backscattering/channeling analysis is shown to reveal an “inverse annealing” effect, where the displacement field increases (∼10×) monotonically with temperature. While this effect has been noted previously by others, it has not been adequately explained. “Inverse annealing” is shown by ion channeling to be anisotropic along different symmetry axes in the lattice. A model is offered that explains this anomaly as arising from microcracks within platelets (hydrogen-related, planar defects) that introduce an anisotropy in the lattice registry. This model will be applied to the study of boron incorporation in Si, which greatly enhances the efficacy of hydrogen-ion cutting. This is easily explained in terms of the model as a change in the orientation rather than the density of the platelets. Lattice location studies using a B(p,α)Be nuclear reaction analysis performed along random and channeling directions is shown to be key in revealing the role of boron in orienting the platelet defects.

SITE MULTIPLICITY OF RARE EARTH IONS IN III-NITRIDES

ABSTRACTThis presentation reviews recent lattice location studies of rare earth (RE) ions in GaN by electron emission channelling (EC) and X-ray absorption fine structure (XAFS) techniques. These studies agree that RE ions at low concentrations (whether they are incorporated during growth or introduced later by ion implantation) predominantly occupy Ga substitutional sites, as expected from considerations of charge equivalence. We combine this result with some examples of the well-documented richness of optical spectra of GaN:RE3+ to suggest that the luminescence of these materials may be ascribed to a family of rather similar sites, all of which feature the REGa defect.

Lattice location studies of rare earth impurities in 3C–, 4H– and 6H–SiC

The lattice location of rare earths Tm in 3C– and 4H–SiC and Yb in 6H–SiC were studied using the emission channeling technique. Radioactive rare earth ions were implanted at the on-line isotope separator ISOLDE at CERN with an energy of 60 keV and fluences of 2×10 13 ions/cm 2. In order to determine the lattice location of the implanted impurities, angular dependent electron yields around certain axes were recorded with conversion electrons arising in the decay 167Tm– 167Er ( t 1/2=9.28 d) and 169Yb– 169Tm ( t 1/2 =30.0 d). The effect of annealing on the normalized electron yields was studied up to 873 K for the 3C– and 4H–SiC samples and up to 1073 K for the 6H–SiC sample. In all cases the implanted rare earths are located on near substitutional silicon sites.

Lanthanide Doped Cubic Boron Nitride

ABSTRACTFirst basic investigations on lanthanide implanted cubic boron nitride were performed with focus on the site of the implanted ions as well as their luminescence behaviour. In order to investigate the lattice sites of lanthanides in c-BN, we implanted single crystal c-BN with radioactive 139Ce ions using the on-line isotope separator ISOLDE at CERN. After the samples were annealed at 1193 K, direct lattice location studies were performed using the conversion electron emission channeling technique and showed a near-substitutional fraction of the implanted ions of at least 10 %. Additionally, poly crystalline c-BN samples were implanted with stable Eu and Tm ions in order to investigate the luminescence properties of triply ionised lanthanides in the c-BN host. It is found that the annealing of the implanted samples at high temperature and high pressure results in strong luminescence of the Eu3+ ions in the orange and moderate luminescence of the Tm3+ ions in the blue. In case of the Eu implanted samples, the luminescence is assigned to the 5D0-7FJ intra-4f electron transitions of Eu3+, in case of the Tm implanted samples, detectable transitions are 1D2-3H6, 1D2-3F4, 1G4-3H6. of Tm3+.

Electron detection by resistive charge division based position sensitive detectors

The use of resistive charge division based solid-state detectors for position sensing of electrons has been studied. The operational conditions having importance for device performance are considered for one- and two-dimensional detectors manufactured by SiTek®. The parameter of main interest has been position resolution. Good linearity with a spatial resolution of 0.2 mm is obtained under optimum conditions. The advantages and limitations of the present approach and alternative techniques that could be considered for individual electron detection are discussed. A possible application of the detector is foreseen in its use for lattice location studies of impurity atoms by emission channeling.

Ion channeling studies of hydrogen in homoepitaxially grown CVD diamond

Abstract Using ion channeling measurements in conjunction with the resonant 1 H( 15 N,αγ) 12 C nuclear reaction or with proton Rutherford backscattering spectrometry we studied the incorporation of hydrogen from the plasma into homoepitaxial (100) and (111) CVD diamond films. The measured hydrogen concentration and the structural defect density of the diamond lattice derived from proton channeling yields were observed to be correlated. Hydrogen lattice location studies for different incident ion channeling directions showed no dominant fraction of H occupying either one of the two theoretically predicted sites. These results suggest that in CVD films with quite high dislocation densities and relative H concentrations above 10 −3 , hydrogen is predominantly incorporated at structural defect sites uncorrelated with the lattice symmetry.

Lattice location studies of indium in Cr2O3

The lattice sites of implanted In atoms in Cr2O3 were investigated by means of electron emission channeling (EC) measurements using 111In probe atoms. EC spectra were recorded for several axes and compared to simulations. Indium atoms are most likely located at near-Cr sites. Small differences in the EC patterns for prompt and delayed electrons may be an indication for displacements of 111Cd emitter atoms following the electron capture decay of In.

Advances in electron emission channeling measurements in semiconductors

This paper reports on recent advances in the application of electron emission channeling to studies of the lattice location of radioactive probe atoms in semiconductors. The introduction of position-sensitive electron detection has resulted in an improvement in the experimental efficiency of this method by two orders of magnitude. Electron emission channeling now is able to carry out detailed lattice location studies, and is especially interesting for cases where conventional ion beam lattice location techniques cannot be applied due to a lack of sensitivity. Characteristic features of electron emission channeling with position-sensitive detection are discussed and illustrated by results on the lattice location of Er in Si and GaAs, and on the lattice sites and stability of implanted transition metals in Si.

Lattice site location studies of ion implanted Li8 in GaN

The lattice sites of ion implanted Li atoms in GaN were studied as a function of implantation temperature between room temperature and 770 K. We measured the channeling and blocking patterns of α-particles emitted in the radioactive decay of implanted Li8 ions to determine the Li lattice sites. Below 700 K Li atoms occupy mainly interstitial sites in the center of the c-axis hexagons at positions c/4 and 3c/4, where c is the lattice constant in c-axis direction. Around 700 K Li starts to diffuse and presumably interacts with vacancies created in the implantation process. This leads to the formation of substitutional Li above 700 K. An activation energy of about 1.7 eV for interstitial Li diffusion was determined.

Electron emission channeling with position-sensitive detectors

Electron emission channeling allows direct lattice location studies of low doses of radioactive atoms implanted in single crystals. For that purpose the anisotropic emission yield of conversion electrons from the crystal surface is measured, most conveniently by use of position-sensitive detectors. We discuss characteristic features of this method, including quantitative data analysis procedures, which are achieved by fitting simulated two-dimensional emission distributions for different lattice sites to the experimental patterns. The capabilities of this approach are illustrated by the case of rare earth atoms (Er, Tm, Yb) in Si, where we were able to do lattice location experiments down to implanted doses which are 150 times lower compared to previous RBS studies.

Lattice location and annealing studies of heavy ion implanted diamond

The lattice location of ion implanted In into type IIa diamond and the annealing of implantation damage was studied with the emission channeling technique. Radioactive 111In was implanted into IIa diamonds with 〈110〉 surface orientation at 300 K, at energies of 120 and 350 keV and at doses between 5 × 10 12 and 5 × 10 13 cm −2. Axial channeling effects of the emitted conversion electrons were measured after annealing to different temperatures up to 1473 K. For implantation doses below 10 13 cm −2 two stages for annealing of implantation defects are observed, one between 300 and 600 K and the other above 1000 K. The appearance of strong channeling effects in all major axial directions after annealing at 1473 K indicates a significant substitutional fraction of In atoms. From a comparison with calculated emission channeling profiles a substitutional fraction of up to 45% was determined. The experimental data are also consistent with a close-to-substitutional fraction of about 50–60% assuming small mean displacements of the In atoms of about 0.1 Å. A significant fraction of In on tetrahedral interstitial sites can be ruled out.

Anomalous electrical deactivation of low concentration rapid thermally annealed arsenic implanted silicon

Lattice location studies of rapid thermally annealed As implanted Si have revealed a previously unreported buried region of stable non-substitutional arsenic-interstitial defects. Profiling analysis indicates that As atoms within these complexes are electrically active. Dissolution of this defect band with increasing annealing time is shown to correlate with further decreases in electrical activation. These results suggest that diffusion and activation of ion implanted As concentrations beneath electrical solubility are mediated on RTA timescales by non-equilibrium implantation-induced point defect distributions.

Shallow junctions for 0.1 μm n-type metal–oxide semiconductor devices

The n+/p junctions for 0.1‐μm‐gate n‐type metal–oxide semiconductor must be no deeper than about 30 nm in order to preserve long‐channel behavior in the enhancement mode metal–oxide semiconductor field‐effect transistor. We report junctions formed by implantation of antimony or arsenic of depth 16–64 nm. They have been characterized by secondary ion mass spectroscopy, Rutherford backscattering spectroscopy lattice location studies, transmission electron microscopy, and electrical measurements.

Lattice-location studies of cerium ions implanted into vanadium single crystals.

The substitutional fraction (${f}_{s}$) of 0.1 at.?Ce in vanadium depends on the lattice temperature during implantation and is 0.73, 0.73, and 0.15 at 5, 77, and 300 K, respectively. Increasing the implanted Ce concentration at 300 K to 3.3 at. ?eads to an increase of ${f}_{s}$ from 0.15 to 0.66. Postirradiation of VCe systems as produced at 300 K with He ions at 77 K leads to an increase of ${f}_{s}$. If the postirradiated systems are warmed up to room temperature ${f}_{s}$ decreases. It is concluded that Ce-vacancy clusters are formed within the prompt cascade regime and by trapping mobile vacancies. Pre- and postimplantation experiments proved that the increase of ${f}_{s}$ with Ce concentration is due to cluster dissolution accompanied by the formation of competing vacancy-trapping centers.

Lattice location and thermal annealing behaviour studies of GaAs single crystals implanted with Co-atoms

Co-atoms have been implanted into n-type GaAs single crystals up to a dose of 2×1015 atoms/cm2. Mossbauer Spectroscopy was used together with Proton Induced X-ray Excitation and Rutherford Backscattering Spectrometry in Channeling geometry to study the recovery of the GaAs-crystal from the implantation damage and the final lattice locations of the Co-atoms. Epitaxial regrowth of the GaAs was found to take place in the annealing temperature region from 300°–450°C. At 900°C rapid thermal annealing an epitaxial Co-phase was found at the surface with the Co-atoms partially blocking the GaAs channel.