The lattice location and hyperfine field of implanted Yb in Fe as a function of annealing temperature

A combined study has been made of the lattice location and hyperfine field of Yb implanted into Fe single crystals. The location has been determined by ion channeling and back-scattering, the hyperfine field by perturbed angular correlation (PAC) measurements on¹⁶⁹Yb (decaying to excited states in¹⁶⁹Tm). The channeling experiments indicate that initially about 60% of the Yb atoms occupy substitutional sites in the Fe lattice, while the remaining atoms are not in any specific crystallographic site. On annealing, Yb migrates from substitutional to non-substitutional sites. No Yb atoms remain substitutional after a 600°C anneal. By making PAC measurements at two temperatures for two - cascades in¹⁶⁹Tm, it is found that the PAC pattern can be described using a combined static and time-dependent magnetic interaction. The PAC results show that the average hyperfine field and relaxation parameter decrease on annealing, and that the field disappears after a 600°C anneal. The correlation between the location and the hyperfine field is discussed. A comparison of the results with previous Mössbauer results for¹⁵¹Gd implanted in Fe, together with relaxation parameter measurements on a¹⁶⁹Yb₂O₃ source, suggests that the non-substitutional Yb is internally oxidized in the Fe host.Work partly carried out while at the Clarendon Laboratory, Oxford, England and Nuclear Physics Division, AERE, Harwell, England.     

Lattice location and dopant behavior of group II and VI elements implanted in silicon

Outdiffusion, lattice location and electrical behavior of Zn, Cd, Hg and Se, Te implanted into silicon at 50 keV were investigated by backscattering and channeling effect of 1 MeV He⁺ ions and by Hall effect and sheet resistivity measurements. All the species exhibited outdiffusion with thermal processing. A significant fraction of Zn, Cd and Hg, when implanted into a substrate of 350°C, occupied regular interstitial lattice sites, while 50–60 per cent of the Se and Te atoms were on substitutional lattice sites. Selenium implanted at room temperature and mercury implanted into a substrate of 350°C exhibited depth dependent lattice location. The implanted layers showed n-type behavior: the maximum value of number of carriers/cm² was less than the number of implanted ions/cm² in all cases. The highest electrical activity was observed for Se corresponding to 25 per cent of the substitutional component.     

Direct evidence for As as a Zn-site impurity in ZnO

Arsenic has been reported in the literature as one of the few p-type dopants in the technologically promising II-VI semiconductor ZnO. However, there is an ongoing debate whether the p-type character is due to As simply replacing O atoms or to the formation of more complicated defect complexes, possibly involving As on Zn sites. We have determined the lattice location of implanted As in ZnO by means of conversion-electron emission channeling from radioactive (73)As. In contrast to what one might expect from its nature as a group V element, we find that As does not occupy substitutional O sites but in its large majority substitutional Zn sites. Arsenic in ZnO (and probably also in GaN) is thus an interesting example for an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system.     

Mössbauer study of 57Fe in GaAs and GaP following 57Mn+ implantation

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken ⁵⁷Fe emission Mössbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive ⁵⁷Mn^?+? ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity–vacancy complexes formed. The Mössbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity–vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T?> 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mössbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.     

In-beam Mössbauer spectroscopy:57Fe in Si and Ge

Fe has been studied in the semiconductors Si and Ge with the Coulomb excitation recoil implantation technique in a wide temperature range. In the case of Fe inSilicon it was found that one third of the implanted atoms land on interstitial sites. The long range diffusion of these atoms could be observed microscopically at temperatures around 600 K. The isomer shift of interstitial Fe in Si was determined. The remaining atoms exhibit a strong quadrupole splitting on disturbed sites. This component seems to relax into a state with higher symmetry above 700 K. InGermanium a similar situation is found. Whereas iron on disturbed sites dominates the spectra, the direct implantation into interstitial sites is also observed below 200 K. At higher temperatures the substitutional position is preferred. The isomer shifts for interstitial and substitutional Fe in Si and in Ge are in good agreement with calculated electron densities.     

Effect of Fe-ion implantation doping on structural and optical properties of CdS thin films

We report on effects of Fe implantation doping-induced changes in structural, optical, morphological, and vibrational properties of cadmium sulfide thin films. Films were implanted with 90 keV Fe⁺ ions at room temperature for a wide range of fluences from 0.1×10¹⁶ to 3.6×10¹⁶ ions cm⁻² (corresponding to 0.38–12.03 at.% of Fe). Glancing angle X-ray diffraction analysis revealed that the implanted Fe atoms tend to supersaturate by occupying the substitutional cationic sites rather than forming metallic clusters or secondary phase precipitates. In addition, Fe doping does not lead to any structural phase transformation although it induces structural disorder and lattice contraction. Optical absorption studies show a reduction in the optical band gap from 2.39 to 2.17 eV with increasing Fe concentration. This is attributed to disorder-induced band tailing in semiconductors and ion-beam-induced grain growth. The strain associated with a lattice contraction is deduced from micro-Raman scattering measurements and is found that size and shape fluctuations of grains, at higher fluences, give rise to inhomogeneity in strain.     

Lattice location and stability of ion implanted Cu in Si

We report on the lattice location of ion implanted Cu in Si using the emission channeling technique. The angular distribution of beta(-) particles emitted by the radioactive isotope 67Cu was monitored following room temperature implantation into Si single crystals and annealing up to 600 degrees C. The majority of Cu was found close to substitutional sites, however, with a significant displacement, most likely 0.50(8) A along the <111> directions towards the bond center position. The activation energy for the dissociation of near-substitutional Cu is estimated to be 1.8-2.2 eV.     

In-beam Mössbauer spectroscopy on single iron atoms in alkali metals

In-beam Mössbauer spectroscopy is applied to study implanted Fe atoms in the alkali metals Li, Na and K. From the Mössbauer parameters we infer that the Fe implants take up substitutional as well as interstitial sites. The strongly increased electron density at the interstitial position is qualitatively explained by the pressure resulting from the small interstitial volume. It is concluded that recently reported local moment formation in these systems cannot be due to substitutional Fe only.     

CEMS study of defect annealing in Fe implanted AlN

An AlN thin film grown on sapphire substrate was implanted with 45 keV ⁵⁷Fe and ⁵⁶Fe ions at several energies to achieve a homogeneous concentration profile of approximately 2.6 at.%. in the AlN film. Conversion electron Mössbauer Spectroscopy data were collected after annealing the sample up to 900 °C. The spectra were fitted with three components, a single line attributed to small Fe clusters, and two quadrupole split doublets attributed to Fe substituting Al in the wurtzite AlN lattice and to Fe located in implantation induced lattice damage. The damage component shows significant decrease on annealing up to 900 °C, accompanied by corresponding increases in the singlet component and the substitutional Fe.     

Formation and migration properties of the rare gases He,Ne, Ar,Kr, and Xe in nickel

The energies of formation and migration of various rare gas-point defect complexes in an f.c.c. nickel lattice have been calculated for He, Ne, Ar, Kr, and Xe. Formation energies of rare gas atoms at interstitial sites are compared with those in substitutional sites. Binding energies are presented for self-interstitials and vacancies trapped to the various rare gas substitutionals. We also present migration energies and migration paths for various rare gas interstitials and substitutionals with and without trapped vacancies and self-interstitials. The migration energies are compared with the breakup energies for the corresponding complexes. We find that divacancy-rare gas complexes are rather stable and will migrate at relatively low energies compared to other substitutional rare gas migration processes.     

The implantation behaviour of indium and silver in iron at low temperature

¹¹¹In and ¹⁰³Ag have been implanted at very low temperatures (30 mK) in iron. Using the nuclear orientation technique it can be shown that the nuclei are ending up almost exclusively in substitutional lattice sites.     

Mössbauer spectra obtained using β − γ coincidence method after 57Mn implantation into LiH and LiD

Highly energetic ⁵⁷Mn (T_1/2 = 1.45 m) was generated by nuclear projectile fragmentation in a heavy-ion accelerator, and implanted into lithium hydride (LiH) and lithium deuteride (LiD) at 578 K. Mössbauer spectroscopy with β ? γ coincidence detection was then carried out on the ⁵⁷Fe obtained from β^?decay of the ⁵⁷Mn to study the time dependence of the site distributions and coordination environments of dilute Fe atoms implanted in the LiH and LiD. The results suggest that the Fe atoms can substitute for either the Li and H or D atoms within 100 ns. Additionally, the displacement behavior of the substitutional ⁵⁷Fe atoms on the lattice sites is discussed.     

Characterization of Cd implanted and annealed GaAs and InP by perturbed angular correlation (PAC) spectroscopy

Investigations of ^111mCd implanted GaAs and InP crystals using the microscopically sensitive perturbed angular correlation technique show that the implanted Cd is incorporated on unperturbed substitutional lattice sites during rapid thermal annealing at significant lower temperatures than for electrical activation is required. In GaAs the higher implantation temperature at 473 K did not show any influence on this annealing stage, whereas as higher implantation dose hinders the annealing. We conclude that not only the local environment of the implant but also the long-range lattice perfection has to be restored for the electrical activation of implants in III-V compound semiconductors.     

Hyperfine interaction of161Dy imprities implated in iron and nickel

In this paper we present a full report on our Mössbauer measurements on implanted sources of¹⁶¹TbFe and¹⁶¹TbNi using the 26.7 keV Mössbauer transition in¹⁶¹Dy. From the measured spectra values were derived for the magnetic and quadrupole interaction strengths of rare earth ions in at least two non-equivalent lattice sites and information is obtained about the relaxation behaviour of these ions.Conclusions are drawn about the lattice location of the implanted ions. Information could also be obtained about the crystalline electric field acting upon the substitutionally implanted rare-earth ions.     

Pulsed electron-beam annealing of high-dose arsenic implanted silicon

The effects of pulsed electron-beam annealing of high-dose As implanted {111} Si single crystals has been studied. The depth distributions and lattice location of the As atoms were obtained using MeV⁴He⁺ backscattering and channeling technique. The implantation energy was 100 keV with a total dose of 3.5·10¹⁶/cm². Above the threshold energy of 0.9 J/cm² the single-crystal transition was observed with about 95% of the As atoms on substitutional lattice sites. This leads to an As concentration of 2·10²¹/cm³ which was demonstrated to be a metastable one.     

In-beam M?ssbauer spectroscopy of 57 Mn implanted into lithium hydride

We measured the temperature dependence of ⁵⁷Fe M?ssbauer spectra obtained after ⁵⁷Mn implantation into polycrystalline LiH with an extremely low implantation dose. Density functional calculations suggested that the Fe atoms were predominantly implanted into both Li and H substitutional sites of the LiH crystal.     

Non-equilibrium dopants incorporation in silicon melted by laser pulses

The rapid solidification of silicon layers melted by high-power laser pulses lead to an enhanced incorporation of implanted dopants in substitutional lattice sites. A review of experimental results, heat and mass transport calculations, is presented together with the latest models for solute redistribution during rapid solidification. Interfacial instabilities, leading to cell structure and other factors limiting the maximum concentration of incorporated dopants are also presented.     

Lattice reordering in Pb implanted Ge crystals

Channeling effect and sheet resistivity techniques have been used to investigate the damage induced by 40 keV Pb implantation in Ge crystals. At 450° the reordering of the Ge lattice occurs simultaneously to the out-diffusion of the implanted Pb atoms while the recovery of the sheet resistivity occurs at higher temperatures. 90% of the implanted atoms still retained in the crystal are located in substitutional sites. Work supported in part by Centro Siciliano di Fisica Nucleare e di Structura della Materia and by Gruppo Nazionale di Struttura della Materia del Consiglio Nazionale delle Ricerche.     

Depth-controlled beta-NMR of 8Li in a thin silver film

Depth-controlled beta-NMR can be used to probe the magnetic properties of thin films and interfaces on a nanometer length scale. A 30 keV beam of highly spin-polarized 8Li+ ions was slowed down and implanted into a 50 nm film of Ag deposited on a SrTiO3 substrate. A novel high field beta-NMR spectrometer was used to observe two well resolved resonances which are attributed to Li occupying substitutional and octahedral interstitial sites in the Ag lattice. The temperature dependence of the Knight shifts and spin relaxation rates are consistent with the Korringa law for a simple metal, implying that the NMR of implanted 8Li reflects the spin suspectibility of bulk metallic silver.     

Hg ION implantation in silicon: Lattice disorder created and hg atom lattice location

Abstract

The lattice disorder produced by 42-keV and 75-keV Hg ions implanted in Silicon at room temperature and the lattice location of the Hg atoms were studied by means of the channeling technique with a 2.0 MeV ⁴He⁺ beam. The damage produced was found to increase linearly with ion dose until a saturation value, connected to the ion range, is reached. The number of Si atoms displaced for Hg ion implanted was evaluated and compared with the theoretical expectation. The substitutional Hg fraction is connected to the disorder produced: the replacement mechanism is discussed.