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Localization of Impuriy Atoms by Channeling of Electrons and Positrons
Abstract
Channeling of decay electrons and positrons emitted from implanted radioactive probes was firstly investigated by Uggerhoj [1] and was among the very early applications of the channeling effect to lattice location.
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Channeling and blocking effects of electrons and positrons emitted from
ion-implanted radioactive In dopants in silicon have been utilized for
lattice location of In in parts-per-million concentrations. A majority
of In atoms occupies substitutional sites after implantation at room
temperature. Defect recovery, which is observed after annealing at 700
K, increases the channeling effects. These results corroborate
conclusions from previous Mössbauer studies on the same system
under identical implantation conditions. The nature of the damage
cascades of the individual implanted impurity probe atoms is discussed.
The influence of atomic strings on the motion through a single crystal of positrons and electrons has been investigated, showing a pronounced dip and peak in yield, respectively, in the axis direction.
The ISOLDE facility at CERN has been utilized for ion implantations of radioactive In isotopes into Cu single crystals for impurity lattice-location studies by means of the channeling effects of emitted charged particles. Conversion electrons with energies around 0.2MeV (112In, 114In), electrons from beta--decays with energies up to 2 MeV (114In, 119In) and positrons (112In) were employed for the channeling measurements. These experiments demonstrate the possibility of combining channeling and Mössbauer effect measurements using 119In under identical experimental conditions.
Radioactive119In+ ions (T
1/2=2.1 min) obtained from the ISOLDE facility at CERN have been implanted into silicon single crystals at room temperature. Mössbauer emission spectra from the 24 keV γ-radiation of the daughter119Sn have been measured by fast resonance-counting technique. Five independent lines, characterized by their hyperfine parameters and Debye temperatures, have been found in the spectra. From the bonding configurations, deduced for the Sn impurity atoms, these are concluded to be located in four different defects in the silicon lattice. Simple models are proposed for the defects.
As implanted ions are brought to rest at relatively low energies, one can anticipate that their lattice sites are predominantly determined by the local chemical bond depending on the band structure of the host crystal and the electronic configuration of the implanted impurities. Consequently, one can expect that for a given pure semiconductor the occupancy of various impurity sites will vary with the valency of the impurity atoms. As an example, impurity sites of several groups of nontransition elements of the Periodic Table implanted in silicon are discussed and compared with recent experimental data. Further, a few simple rules concerning the behaviour of implanted impurities in silicon are formulated giving some insight into the nature of the electronic structure of implanted semiconductors.
Impurity defect structures in amorphous and crystalline silicon have been created by the ion implantation of radioactive 119In at room temperature. The defects have been studied by Mössbauer spectroscopy on the 24 keV gamma radiation of the daughter 119Sn. Structurally similar complex defects are concluded to be formed in both phases of the silicon host. The nature of the complex defects depends on the species of implanted impurities. The fraction of complex defects in crystalline silicon increases with increasing implanted dose in the dose range of 1011 − 1015 atoms/cm2. No pronounced discontinuity is observed for the critical dose (⪆ 1013 atoms/cm2), where the implanted host volume is amorphised. The implications of these results on the question of a characterisation of the amorphous phase of semiconductors by Mössbauer spectroscopy on implanted impurities will be discussed.
Lattice damage after implantation of111In in Ni has been studied applying the DPAC technique to the 171 245 keV gamma-ray cascade in the daughter nucleus111Cd. Implantations were carried out at 10 K and at 300 K. The low temperature implantation yields a higher regular substitutional fraction (80%) than the room temperature implantation (40%). The annealing behaviour of both implants above RT is the same. In addition, two distinct defect-associated sites were observed in isochronal annealing sequences. A microscopic model for these defects is presented, which takes into account magnetic and electric hyperfine interaction strengths, binding energies and site populations as a functions of temperature.
With the use of conversion electrons emitted during the decay of 111In atoms diffused into a copper single crystal, it is shown that the electrons are steered by lattice rows and that the impurities are localized at substitutional sites. The damage produced by implantation of the radioactive atoms was investigated in a simultaneously performed channeling and perturbed-γγ angular-correlation experiment using 111In as probe atom. The formation of defect clusters at the probes' site can be observed by both techniques.
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.
Heavy ions from all groups of the periodic system have been implanted at keV energies into Si at room temperature. The samples have been analyzed in their as-implanted state by high resolution ion backscattering of 0.5 MeV 4He ions. The results show that only elements from groups IIIa, IVa and Va have dominant substitutional occupation, whereas in all other cases interstitial sites are largely preferred. It is concluded that chemical effects govern the selection of lattice sites.
The channeling of conversion electrons with energies of 145 and 219 keV emitted from 111In embedded in a Cu single crystal was investigated and used to localize the In impurities on substitutional sites after implantation. Electron channeling was performed simultaneously with perturbed γγ-angular correlation (PAC) experiments using the γγ-cascade in the decay of 111In to study the radiation damage produced by the implantation of the probe atoms. The channeling effect is influenced by the formation of defects at the impurities as indicated by the PAC.
Electromagnetic mass separation applied on-line to accelerators and nuclear reactors is now a standard technique for producing preselected isotopic beams (A, Z selection) of nuclear reaction products. The development, performance and anatomy of a large on-line isotope separator facility, the CERN-ISOLDE, is discussed. As a result of recent technical developments it is now possible to study individual nuclei of about 40 elements, in many cases out to where the limits of nucleon binding are approached and half-lives become as short as 10 ms. It is shown that the nuclear reaction processes induced with the high-intensity several hundred MeV proton beam can provide secondary radioactive beams in almost all regions of the nuclidic chart with intensities which are not matched by any other method. The intense beams of 108–1011 atoms/s have opened up a number of new experimental possibilities like laser spectroscopy on radioactive atoms, radioactive targets for nuclear reaction spectroscopy, and precision X-ray shift measurements.
Defect migration and accretion are observed in 111doped Ni, using perturbed gamma-gamma angular correlations. Our samples were damaged by variable doses of proton irradiations and deformation at 200 K, well below resistivity stage III. Subsequent isochronal annealing extended to 900 K. When combined with previous work on ion-implanted Ni, the present work leads to a plausible recovery model in Ni which assumes vacancies migrate in stage III. The model includes the free migration and trapping of vacancy defects in the range 270
Winter in “Vacancies and Interstitials in Metals and Alloys
- B Besold
- E Danielsen
- H Hofsäss
- G Lindner
- J W Petersen
- E Recknagel
- M Søndergaard
- G Weyer