Publications (18)31.94 Total impact
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Article: Specific features of transmutational doping of 30Si-enriched silicon crystals with phosphorus: Studies by the method of electron spin resonance
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ABSTRACT: Electron spin resonance (ESR) is used to study the neutron transmutation doping of silicon crystals enriched with 30Si isotope: phosphorus donors and radiation defects produced in the course of transmutational doping are observed. The ESR signals related to the phosphorus uncontrolled impurity in 30Si before transmutational doping (the P concentration is ∼1015 cm−3) and phosphorus introduced by neutron irradiation with doses ∼1 × 1019 cm−2 and ∼1 × 1020 cm−2 (the P concentrations are ∼5 × 1016 and ∼7 × 1017 cm−3, respectively) are studied. As a result of drastic narrowing of the phosphorus ESR lines in 30Si, the intensity of lines increased appreciably, which made it possible to measure the phosphorus concentration in the samples with a small volume (down to 10−6 mm−3). The methods for determining the concentration of P donors from hyperfine structure in the ESR spectra of isolated P atoms, exchange-related pairs, and clusters that consist of three, four, and more P donors are developed. In the region of high concentrations of P donors, in which case the hyperfine structure disappears, the concentration of P donors was estimated from the exchange-narrowed ESR line.Semiconductors 04/2012; 40(8):901-910. · 0.63 Impact Factor -
Article: Towards 0.99999 28Si
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ABSTRACT: a b s t r a c t A new approach for producing high-purity silicon with isotopic enrichment of 28 Si isotope is reported. The methods of centrifugal enrichment were modified to obtain the initial gaseous silicon tetrafluoride with a record-breaking enrichment of 0.99999664(11) with respect to 28 Si. The effective conversion of silicon tetrafluoride into elementary silicon with minimal isotopic dilution was achieved in an electron cyclotron resonance discharge plasma, sustained by gyrotron microwave radiation with a frequency of 24 GHz. We have experimentally demonstrated the deposition of the layers of microcrystalline 28 Si with enrichment of 0.999986 ± 0.000003, which is the best result at the present time.Solid State Communications 01/2012; 152:455-457. · 1.65 Impact Factor -
Article: Photoluminescence of deep defects involving transition metals in Si: New insights from highly enriched 28Si
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ABSTRACT: Deep luminescence centers in Si associated with transition metals have been studied for decades, both as markers for these deleterious contaminants, as well as for the possibility of efficient Si-based light emission. They are among the most ubiquitous luminescence centers observed in Si, and have served as testbeds for elucidating the physics of isoelectronic bound excitons, and for testing ab-initio calculations of defect properties. The greatly improved spectral resolution resulting from the elimination of inhomogeneous isotope broadening in the recently available highly enriched 28Si enabled the extension of the established technique of isotope shifts to the measurement of isotopic fingerprints, which reveal not only the presence of a given element in a luminescence center, but also the number of atoms of that element. This has resulted in many surprises regarding the actual constituents of what were thought to be well-understood deep luminescence centers. Here we summarize the available information for four families of centers containing either four or five atoms chosen from (Li, Cu, Ag, Au, Pt). The no-phonon transition energies, their isotope shifts, and the local vibrational mode energies presented here for these deep centers should prove useful for the still-needed theoretical explanations of their formation, stability and properties.Journal of Applied Physics 10/2011; 110(8):081301-081301-25. · 2.17 Impact Factor -
Article: Isotopic fingerprints of Pt-containing luminescence centers in highly enriched^{28} Si
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ABSTRACT: Recently we have shown that the reduction in the photoluminescence linewidth of many deep luminescence centers in highly enriched 28Si results in well-resolved isotopic fingerprints. This allows for a better characterization of a defect center, as not only the involvement of a specific element but also the number of atoms of that element within the complex can be determined. Surprisingly, we have found that many well-known luminescence centers have a different composition than originally supposed. In addition, we have found a large number of four- and five-atom luminescence centers involving the elements Cu, Au, and Li. Here we introduce series of four- and five-atom deep luminescence centers involving a single Pt atom together with Cu and Li, similar to what has been seen previously for Au-containing luminescence centers.Physical Review B 01/2010; 81:235217. · 3.69 Impact Factor -
Article: Isotopic fingerprints of gold-containing luminescence centers in 28Si
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ABSTRACT: We have recently shown that the dramatic reduction in linewidth of many deep luminescence centers in highly enriched 28Si can lead to the observation of isotopic fingerprints, revealing not only that a specific element is involved in the defect complex, but also the number of atoms of that element. This has led to many surprises regarding the actual constituents of supposedly well known luminescence centers, as well as the discovery of new members of a family of four-atom centers where the constituents can be chosen from Cu, Ag, Au and Li. Obtaining the isotopic fingerprint of Au is problematic, since only 197Au is stable, but we have now used the relatively long-lived 195Au to reveal the presence, and the number, of Au atoms in several of these centers. We find a series of four-atom centers containing one Au plus Cu and/or Li. Surprisingly, the Au isotopic fingerprint also reveals a series of five-atom centers containing a single Au plus Cu and/or Li. Further evidence for the ubiquity of these four- and five-atom defects is provided by two previously observed Pt-related centers, with luminescence at 884 and 777 meV, which are present in these samples due to the decay of 195Au to 195Pt. In addition to Pt, these centers are found to contain three and four Cu atoms, respectively.Physica B Condensed Matter 01/2009; 404(23–24):5050 - 5053. · 1.06 Impact Factor -
Article: High-purity single-crystal monoisotopic silicon-28 for precise determination of Avogadro’s number
Doklady Chemistry 06/2008; 421(1):157-160. · 0.31 Impact Factor -
Article: Reduction of the linewidths of deep luminescence centers in 28Si reveals fingerprints of the isotope constituents.
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ABSTRACT: Dramatic reductions of the linewidths of well-known deep centers in 28Si reveal "isotopic fingerprints" of the constituents. The approximately 1014 meV Cu center, thought to be either a Cu pair or an isolated Cu, is shown to contain four Cu atoms, and the approximately 780 meV Ag center is shown to contain four Ag. The approximately 944 meV ;{*}Cu center, thought to be a different configuration of a Cu pair, in fact contains three Cu and one Ag, and a new two-Cu two-Ag center is found. The approximately 735 meV center, previously assigned to Fe, actually contains Au and three Cu. This suggests a family of four-atom (Cu, Ag, Au) centers.Physical Review Letters 05/2008; 100(17):177402. · 7.37 Impact Factor -
Article: Peculiarities of neutron-transmutation phosphorous doping of 30Si enriched SiC crystals: Electron paramagnetic resonance study
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ABSTRACT: We have obtained a high concentration of P donor dopants in 6H‐SiC enriched with 30Si and irradiated with thermal neutrons. It was established that annealing at a relatively low temperature of 1300 °C, i.e., 500–600 °C lower than that used for annealing SiC with the natural isotope composition after neutron-transmutation doping, gives rise to an electron paramagnetic resonance (EPR) signal corresponding to three different shallow P (sP) donors with large hyperfine interactions. The correlated changes of these sP centers in all the annealing experiments and the similarities to the spectra of shallow N donors demonstrate that these sites have shallow donor levels and a similar electronic structure and that they belong to different lattice sites: two quasicubic and hexagonal. The phosphorus at these three sites is suggested to occupy the C position. Simultaneously the low-temperature EPR signal from another set of P-related donor centers having a small, strongly anisotropic hyperfine interaction is observed. It is suggested that phosphorus in these centers occupies the Si position. Annealing at 1800 °C yields opposite changes in the concentrations of the two types of P-related donor centers: The EPR signals of sP centers disappear, while the intensity of the low-temperature EPR spectra of P donors considerably increases. Thus, the phosphorus at the C position is established to be unstable and annealing above 1700 °C causes P at the C site to move to the Si site. This process is vacancy mediated, as the temperature of this process is shown to depend on the thermal stability of intrinsic defects produced by neutron irradiation, whose concentration is proportional to the neutron irradiation dose.Journal of Applied Physics 09/2007; 102(6):063713-063713-8. · 2.17 Impact Factor -
Article: Shallow Impurity Absorption Spectroscopy in Isotopically Enriched Silicon
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ABSTRACT: Karaiskaj et al. showed that the isotopic randomness present in natural Si (natSi) causes inhomogeneous broadening of many of the ground state to excited state infrared absorption transitions of the shallow donor phosphorous and acceptor boron. This was surprising since it was thought that the observed linewidths of shallow impurities in silicon are at their fundamental lifetime limit. We report improved high‐resolution infrared absorption studies of these impurities in isotopically enriched 28Si, 29Si and 30Si. The new data improves on the linewidths of earlier spectra due to reduced concentration broadening. Some of the transitions in 28Si show the narrowest FWHM ever reported for shallow donor and acceptor absorption transitions. © 2007 American Institute of PhysicsAIP Conference Proceedings. 04/2007; 893(1):231-232. -
Article: Optical detection and ionization of donors in specific electronic and nuclear spin States.
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ABSTRACT: We resolve the remarkably sharp bound exciton transitions of highly enriched 28Si using a single-frequency laser and photoluminescence excitation spectroscopy, as well as photocurrent spectroscopy. Well-resolved doublets in the spectrum of the 31P donor reflect the hyperfine coupling of the electronic and nuclear donor spins. The optical detection of the nuclear spin state, and selective pumping and ionization of donors in specific electronic and nuclear spin states, suggests a number of new possibilities which could be useful for the realization of silicon-based quantum computers.Physical Review Letters 01/2007; 97(22):227401. · 7.37 Impact Factor -
Article: Large-scale production of highly enriched 28Si for the precise determination of the Avogadro constant
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ABSTRACT: An attempt is described to replace the present definition of the kilogram with the mass of a certain number of silicon atoms. A prerequisite for this is that the Avogadro constant, NA, is determined with a relative uncertainty of better than 2 × 10−8. For the determination, silicon crystals are used. However, the difficulty arising thereby is the measurement of the average molar mass of natural Si. Consequently, a worldwide collaboration has been launched to produce approximately a 5 kg 28Si single crystal with an enrichment factor greater than 99.985% and of sufficient chemical purity so that it can be used to determine NA with the targeted relative measurement uncertainty mentioned above. In the following, the first successful tests of all technological steps will be reported (enrichment of SiF4, distillation into silane and chemical purification, chemical vapour deposition of polycrystalline 28Si, floating zone growth of a dislocation-free single crystal) and new equipment for the production of high-purity 28Si with an enrichment of not less than 99.99% will be described. All steps are well defined by a Technical Road Map (TRM28) and all key results are measured by new mass spectrometric, IR spectroscopic and other chemical and physical methods, such as Hall effect, photoluminescence, laser scattering and x-ray topographic methods (TRM for Analytical Monitoring and Certification, TRM28-AMC). The initial enrichment of the gas is >0.999 95 and the depletion during the entire process is <0.000 05. The isotopic homogeneity is checked by natural Si crystal growth and does, in the enriched sphere, not exceed 5 × 10−10, relatively. The C content of the final material is less than 1015 atoms cm−3 and the specific resistance is 400–1000 Ω cm.Measurement Science and Technology 06/2006; 17(7):1854. · 1.49 Impact Factor -
Article: Neutron transmutation doping of silicon 30Si monoisotope with phosphorus
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ABSTRACT: Phosphorus-doped silicon 30Si monoisotope samples with a highly homogeneous impurity distribution at a concentration of 5 × 1016 cm−3 were obtained for the first time by means of neutron transmutation doping.Technical Physics Letters 01/2006; 32(6):550-553. · 0.56 Impact Factor -
Article: Probing of the shallow donor and acceptor wave functions in silicon carbide and silicon through an EPR study of crystals with a modified isotopic composition
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ABSTRACT: The spatial distributions of the unpaired-electron wave functions of shallow N donors in SiC crystals and of shallow P and As donors in silicon crystals were determined by studying crystals with a modified content of the 29Si and 13C isotopes having a nonzero nuclear magnetic moment. As follows from the present EPR and available ENDOR data, the distribution of donor electrons in SiC depends substantially on the polytype and position in the lattice; indeed, in 4H-SiC, the unpaired electrons occupy primarily the Si s and p orbitals, whereas in 6H-SiC these electrons reside primarily in the s orbitals of C. The electron distributions for the N donor in the hexagonal position, which has a shallow level close to that obtained for this material in the effective-mass approximation, and for the donor occupying the quasi-cubic position differ substantially. The EPR spectrum of N in quasi-cubic positions was observed to have a hyperfine structure originating from a comparatively strong coupling with the first two coordination shells of Si and C, which were unambiguously identified. The effective-mass approximation breaks down close to the N donor occupying the quasi-cubic position, and the donor structure and the donor electron distribution become less symmetric. In silicon, reduction of the 29Si content brought about a substantial narrowing of the EPR line of the shallow P and As donors and an increase in the EPR signal intensity, as well as a noticeable increase in the spin-lattice relaxation time T 1. This offers the possibility of selectively studying these spectra by optically exciting a region of the crystal in order to shorten T 1 and thereby precluding EPR signal saturation only in the illuminated part of the material. This method may be used to advantage in developing materials for quantum computers based on donors in silicon and SiC.Physics of the Solid State 11/2005; 47(12):2219-2232. · 0.71 Impact Factor -
Article: Isotope-pure silicon layers grown by MBE
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ABSTRACT: Molecular-beam epitaxy with a solid source was used to grow silicon layers enriched with 28Si and 30Si isotopes to 99.93 and 99.34%, respectively. Secondary-ion mass spectrometry and Raman scattering spectroscopy were applied to demonstrate the high isotopic purity and crystal perfection of the layers obtained.Semiconductors 11/2002; 36(12):1400-1402. · 0.63 Impact Factor -
Article: Single-frequency laser spectroscopy of the boron bound exciton in^{28} Si
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ABSTRACT: While the first comparison of shallow bound exciton photoluminescence between natural Si and highly enriched 28Si dramatically demonstrated the importance of inhomogeneous isotope broadening, the transitions in 28Si were in fact too narrow to be resolved with the then available instrumental resolution of 0.014 cm−1. We report results for the boron bound exciton transition in highly enriched 28Si using a novel apparatus for photoluminescence excitation spectroscopy based on a tuneable single-frequency laser source with sub-MHz resolution. Twenty well-resolved doublets, exhibiting a 10B–11B isotope splitting, are observed in the new spectra for 28Si with isotopic enrichment >99.99%. Linewidths as narrow as 0.0012 cm−1 (150 neV) full width at half maximum are observed for the most highly enriched sample.Phys. Rev. B. 80(19). -
Article: High resolution photoluminescence of sulphur- and copper-related isoelectronic bound excitons in highly enriched 28Si
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ABSTRACT: We present a study of excitons bound to sulphur- and copper-related isoelectronic centres in highly enriched 28Si. The S-related centre, which has been shown to have two configurations, SA and SB, was believed to consist of a substitutional sulphur atom paired with an interstitial copper atom. High resolution photoluminescence (PL) emissions from the no-phonon transition reveal fine structure not observable in natural silicon. In both 28Si:natS and 28Si:34S, low temperature PL reveals at least 18 distinct components of the system, including a triplet splitting seen in natSi:natS by optical detection of magnetic resonance. Investigation of the effect of copper isotopic composition on the system shows that the centre contains at least three copper atoms. We also present results of the copper isotope effect on the 943.7 meV *Cu00 system in 28Si and show that three Cu atoms contribute to the Cu isotope shift of *Cu00.Physica B Condensed Matter · 1.06 Impact Factor -
Article: Direct observation of the donor nuclear spin in a near-gap bound exciton transition: P in highly enriched Si
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ABSTRACT: We report on ultrahigh resolution studies of the bound exciton states associated with the shallow acceptor B and the shallow donor P in highly enriched 28 Si using a tuneable single frequency laser to perform photoluminescence excitation spectroscopy. The linewidths and fine structure of the transitions, which were too narrow to be resolved previously using an available photoluminescence apparatus, are now fully revealed. The P bound exciton transition shows a complicated additional structure, which the Zeeman spectroscopy demonstrates to be a result of the splitting of the donor ground state by the hyperfine interaction between the spin of the donor electron and that of the 31 P nucleus. The 31 P nuclear spin populations can thus be determined, and hopefully modified, by optical means. The predominant Auger recombination channel of these bound excitons is used to observe the same resolved hyperfine transitions in the photocurrent spectrum. This demonstrates that donors in specific electronic and nuclear spin configurations can be selectively photoionized. Possible applications of these results to quantum computing and quantum information systems are discussed. © 2007 American Institute of Physics. -
Article: Can highly enriched 28Si reveal new things about old defects?
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ABSTRACT: Recent studies have demonstrated remarkable improvements in the spectroscopy of shallow impurities by using highly enriched 28Si to eliminate the inhomogeneous isotope broadening inherent in natural Si. Here, we show that similar dramatic improvements in the linewidths of electronic transitions of two well-known deep levels can be achieved in highly enriched 28Si. New fine structure is revealed in the absorption spectrum of the Se double donor, and one of the transitions of Se+ becomes so sharp that a splitting due to a hyperfine coupling with the I=1/2 nuclear spin is revealed for 77Se+. Under an applied magnetic field, the electronic and nuclear spins can be individually determined leading to the possibility of applications in quantum computing. The photoluminescence transitions of the well-known 1014 meV Cu-related luminescence center also sharpen dramatically in 28Si, allowing fine structure due to Cu isotope shifts to be resolved. Current models disagree as to whether this center contains one or two Cu atoms, but our results clearly demonstrate the involvement of four Cu atoms.Physica B Condensed Matter · 1.06 Impact Factor
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Institutions
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2007–2008
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Simon Fraser University
- Department of Physics
Burnaby, British Columbia, Canada
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