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Sökning: WFRF:(Svensson J) > Luleå tekniska universitet

  • Resultat 1-6 av 6
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1.
  • Nylandsted Larsen, A., et al. (författare)
  • Tin-vacancy acceptor levels in electron-irradiated n-type silicon
  • 2000
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:7, s. 4535-4544
  • Tidskriftsartikel (refereegranskat)abstract
    • Si crystals (n-type, fz) with doping levels between 1.5×1014 and 2×1016 cm-3 containing in addition ∼1018 Sn/cm3 were irradiated with 2-MeV electrons to different doses and subsequently studied by deep level transient spectroscopy, Mössbauer spectroscopy, and positron annihilation. Two tin-vacancy (Sn-V) levels at Ec-0.214 eV and Ec-0.501 eV have been identified (Ec denotes the conduction band edge). Based on investigations of the temperature dependence of the electron-capture cross sections, the electric-field dependence of the electron emissivity, the anneal temperature, and the defect-introduction rate, it is concluded that these levels are the double and single acceptor levels, respectively, of the Sn-V pair. These conclusions are in agreement with electronic structure calculations carried out using a local spin-density functional theory, incorporating pseudopotentials to eliminate the core electrons, and applied to large H-terminated clusters. Thus, the Sn-V pair in Si has five different charge states corresponding to four levels in the band gap.
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2.
  • Bathen, M. E., et al. (författare)
  • Anisotropic and plane-selective migration of the carbon vacancy in SiC : Theory and experiment
  • 2019
  • Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 100:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigate the migration mechanism of the carbon vacancy (VC) in silicon carbide (SiC) using a combination of theoretical and experimental methodologies. The VC, commonly present even in state-of-the-art epitaxial SiC material, is known to be a carrier lifetime killer and therefore strongly detrimental to device performance. The desire for VC removal has prompted extensive investigations involving its stability and reactivity. Despite suggestions from theory that VC migrates exclusively on the C sublattice via vacancy-atom exchange, experimental support for such a picture is still unavailable. Moreover, the existence of two inequivalent locations for the vacancy in 4H-SiC [hexagonal, VC(h), and pseudocubic, VC(k)] and their consequences for VC migration have not been considered so far. The first part of the paper presents a theoretical study of VC migration in 3C- and 4H-SiC. We employ a combination of nudged elastic band (NEB) and dimer methods to identify the migration mechanisms, transition state geometries, and respective energy barriers for VC migration. In 3C-SiC, VC is found to migrate with an activation energy of EA=4.0 eV. In 4H-SiC, on the other hand, we anticipate that VC migration is both anisotropic and basal-plane selective. The consequence of these effects is a slower diffusivity along the axial direction, with a predicted activation energy of EA=4.2 eV, and a striking preference for basal migration within the h plane with a barrier of EA=3.7 eV, to the detriment of the k-basal plane. Both effects are rationalized in terms of coordination and bond angle changes near the transition state. In the second part, we provide experimental data that corroborates the above theoretical picture. Anisotropic migration of VC in 4H-SiC is demonstrated by deep level transient spectroscopy (DLTS) depth profiling of the Z1/2 electron trap in annealed samples that were subject to ion implantation. Activation energies of EA=(4.4±0.3) eV and EA=(3.6±0.3) eV were found for VC migration along the c and a directions, respectively, in excellent agreement with the analogous theoretical values. The corresponding prefactors of D0=0.54cm2/s and 0.017cm2/s are in line with a simple jump process, as expected for a primary vacancy point defect.
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4.
  • Larsson, Jan, et al. (författare)
  • “Painting of Fourth” in different evolutionary lineages of Drosophila suggests chromosome specific gene regulation
  • 2004
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 101:26, s. 9728-9733
  • Tidskriftsartikel (refereegranskat)abstract
    • Painting of fourth (POF) is a chromosome-specific protein in Drosophila and represents the first example of an autosome-specific protein. POF binds to chromosome 4 in Drosophila melanogaster, initiating at the proximal region, followed by a spreading dependent on chromosome 4-specific sequences or structures. Chromosome-specific gene regulation is known thus far only as a mechanism to equalize the transcriptional activity of the single male X chromosome with that of the two female X chromosomes. In Drosophila, a complex including the male-specific lethal proteins, "paints" the male X chromosome, mediating its hypertranscription, explained to some extent by the acetylation of lysine 16 on histone H4. Here, we show that Pof is essential for viability in both sexes and for female fertility. POF binding to an autosome, the F element, is conserved in genus Drosophila, indicating functional conservation of the autosome specificity. In three of nine studied species, POF binds to the male X chromosome. When bound to the male X, it also colocalizes with the dosage compensation protein male-specific lethal 3, suggesting a relationship to dosage compensation. The chromosome specificity is determined at the species level and not by the amino acid sequence. We argue that POF is involved in a chromosome-specific regulatory function
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5.
  • Markevich, V.P., et al. (författare)
  • Reconfigurations and diffusion of trivacancy in silicon
  • 2012
  • Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 107:15, s. 2974-2977
  • Tidskriftsartikel (refereegranskat)abstract
    • Disappearance of the divacancy (V2) and trivacancy (V3) complexes upon isochronal and isothermal annealing of electron irradiated Si:O crystals has been studied by means of deep level transient spectroscopy. The annealing studies have shown that the V2 and V3 defects are mobile in Si at T>200 °C and in oxygen-rich material are trapped by interstitial oxygen atoms so resulting in the appearance of V2O and V3O defects. The activation energies for diffusion of the V2 and V3 centers have been determined. Density functional modeling calculations have been carried out to investigate the migration and reorientation mechanisms of V3 in large silicon supercells. It is proposed that these comprise a sequence of transformations between V3(D3) and V3(C2v) configurations.
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6.
  • Vaqueiro-Contreras, Michelle, et al. (författare)
  • Powerful recombination centers resulting from reactions of hydrogen with carbon–oxygen defects in n-type Czochralski-grown silicon
  • 2017
  • Ingår i: Physica Status Solidi. Rapid Research Letters. - : John Wiley & Sons. - 1862-6254 .- 1862-6270. ; 11:8
  • Tidskriftsartikel (refereegranskat)abstract
    • It has been acknowledged for over 50 years that treatments with hydrogen can improve silicon semiconductor devices. In recent years, these have been used to an advantage in silicon solar cells reducing the loss of photo-generated carriers at the silicon surface or at the silicon interface with dielectrics. However, we have found that in some types of silicon the in-diffusion of hydrogen can result in the formation of powerful recombination centers composed of carbon, oxygen, and hydrogen which reduce the carrier lifetime and ultimately the efficiency of solar cells made from such material
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