J. Linnros

KTH Royal Institute of Technology, Tukholma, Stockholm, Sweden

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Publications (130)233.71 Total impact

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    ABSTRACT: A dielectric matrix with embedded Si-nanoparticles may show strong luminescence depending on nanoparticles size, surface properties, Si-excess concentration and matrix type. Ion implantation of Si ions with energies of a few tens to hundreds of keV in a SiO2 matrix followed by thermal annealing was identified as a powerful method to form such nanoparticles. The aim of the present work is to optimize the synthesis of Si-nanoparticles produced by ion implantation in SiO2 by employing MeV ion irradiation as an additional annealing process. The luminescence properties are measured by spectrally resolved photoluminescence including PL lifetime measurement, while X-ray reflectometry, atomic force microscopy and ion beam analysis are used to characterize the nanoparticle formation process. The results show that the samples implanted at 20%-Si excess atomic concentration display the highest luminescence and that irradiation of 36 MeV 127I ions affects the luminosity in terms of wavelength and intensity. It is also demonstrated that the nanoparticle luminescence lifetime decreases as a function of irradiation fluence. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    No preview · Article · Aug 2015 · physica status solidi (c)
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    ABSTRACT: In this paper, an alternative method to characterize the interface between 4H polytype of Silicon Carbide (4H-SiC) and passivating dielectric layers is established. The studies are made on dielectric-semiconductor test structures using Al2O3 as dielectric on 4H-SiC n-type epitaxial layers. Samples with different pre- and post-dielectric deposition preparations have been fabricated on epilayers of varying thicknesses. Effective lifetimes (τeff) of all the samples were measured by an optical pump-probe method utilizing free carrier absorption (FCA) to analyse the influence of the 4H-SiC/dielectric interface on charge carrier recombination. The relative contribution to τeff from the surfaces increases with decreasing epilayer thickness, and by analysing the data in combination with numerical modelling, it is possible to extract values of the surface recombination velocities (SRVs) for interfaces prepared in different ways. For instance, it is found that SRV for a standard cleaning procedure is 2 × 106 cm/s compared to a more elaborate RCA process, yielding a more than 50 times lower value of 3.5 × 104 cm/s. Furthermore, the density of interface traps (Dit) is extracted from capacitance-voltage (CV) measurements using the Terman method and a comparison is made between the SRV extracted from FCA measurements and Dits extracted from CV measurements on the same structures fabricated with metal contacts. It is observed that the SRV increase scales linearly with the increase in Dit. The strong qualitative correlation between FCA and CV data shows that FCA is a useful characterization technique, which can also yield more quantitative information about the charge carrier dynamics at the interface.
    Full-text · Article · Mar 2015 · Journal of Applied Physics
  • K Gulbinas · V Grivickas · P Grivickas · J Linnros
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    ABSTRACT: Experiments are presented that reveal an efficient optical energy conversion from the visible to the infrared wavelengths range as a result of photo-acoustic response (PAR) after light pulse incites onto the free surface of TlGaSe2 crystal. Excitation was carried out with a tunable wavelength of ns-pulse laser and the PAR was detected laterally with a focused cw- probe. The observed properties can be related to variety of successive factors: high electron- hole-phonon deformation potential, a high factor of refraction coefficient dependency on pressure, the absence of surface recombination and the band filling effect, in relation with low absorption coefficient due to the forbidden direct-band optical transition in TlGaSe2. All these ensure that the acoustic energy remain well confined under a wide pulse power and energy range suggesting that TlGaSe2 is a promising material for dynamic optical energy conversion.
    No preview · Article · Nov 2014 · IOP Conference Series Materials Science and Engineering
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    I. Sychugov · J. Valenta · K. Mitsuishi · J. Linnros
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    ABSTRACT: The results of low-temperature photoluminescence characterization of single silicon nanocrystals prepared from highly doped silicon-on-insulator wafers are presented. The effect of B, P, As, and Sb impurities on ensemble as well as individual emission spectra are determined by comparison with the line shapes of undoped nanocrystals. From the statistical analysis of the luminescence spectra, the donor ionization energies for nanocrystals emitting in the range of 1.5–2.0 eV are estimated to be 140–200 meV, while the exciton-impurity binding energy for As- and Sb-doped nanocrystals is found to be about 40–45 meV.
    Full-text · Article · Aug 2012 · Physical review. B, Condensed matter
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    I. Sychugov · J. Valenta · K. Mitsuishi · M. Fujii · J. Linnros
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    ABSTRACT: Optical transitions in silicon nanocrystals with different surface passivations were probed at low temperatures on a single-particle level. A type of quasidirect recombination process, different from the quantum-confined exciton transition, is identified. The luminescence spectra have different emission energies, but the contribution of a no-phonon transition is significantly higher than expected from the quantum-confinement model. Its relative strength was found to be temperature dependent, suggesting spatial localization of excitons as a possible origin.
    Full-text · Article · Sep 2011 · Physical review. B, Condensed matter
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    ABSTRACT: Fine conducting features have been produced on Si and SiO2 substrates by irradiation of spin-on palladium acetate, [Pd(O2CCH3)2]3 films with a submicron focused ion beam. The exposures were made with a 20 keV Ga+, focused to a 0.2 micrometer spot. Electrical conductivity measuremnents were made on the resultant features as a function of ion dose for linewidths of one and ten micrometers. The sheet conductivity in the two cases was comparable and increased dramatically in the dose range between 2×1014 and 5×1014 ions/cm2. The conductivity of the exposed lines was further increased after heating in a hydrogen atmosphere. Measurements of carbon and oxygen content indicate that even at the highest ion doses a significant amount of organic material remains. Results are compared to those for 2 MeV He+ and Ne+ broad beam exposures. Potential applications are also discussed.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Ion-beam induced epitaxial crystallization of thin amorphous silicon layers at {100} and {110} crystalline/amorphous interfaces exhibits no orientation dependencies, whereas at a {111} crystalline/amorphous interface a weak orientation dependency relative to thermal-induced epitaxial crystallization is observed. This behavior supports an interpretation in which the thermal crystallization process is dominated by the need to form interfacial defects and/or growth sites and in the ion-beam experiment this formation process ocurrs athermally. It is thought that the observed orientation dependent regrowth on a {111} substrate relative to a {100} (or {110}) substrate is associated with the special correlated atomic sequencing which is believed to control solid-phase epitaxial crystallization at a {111) crystalline/amorphous interface.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • R. G. Elliman · J. Linnros · W. L. Brown
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    ABSTRACT: Fixed fluence ion irradiation of silicon is shown to produce either defected crystal or amorphous silicon depending on the ion flux employed. The amorphous threshold flux, defined as the minimum flux required to generate a continuous amorphous layer for a fixed fluence irradiation, is measured as a function of irradiation temperature. This critical flux for amorphization is shown to satisfy an Arrhenius expression with a unique activation energy of ∼1.2eV, which corresponds to the migration/dissociation energy of the silicon divacancy. These observations lead to the conclusion that the stability of the silicon divacancy controls the competition between defect production and dynamic defect annealing, and hence the crystalline to amorphous phase transformation.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library

  • No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: We have measured the radiation-enhanced diffusion of Au in amorphous Si in the temperature range 77–700 K. Gold was implanted to depths of 500Å at concentrations of an atomic %. The samples were than amorphized to depths of -2μm using MeV Ar implants at liquid nitrogen temperature. Radiation-enhanced diffusion was induced by a 2.5 MeV Ar beam at doses of 2×1016−2×1017/cm2 and dose rates of 7×1012−7×1013/cm2sec. The diffusion coefficients show three well defined regions. At temperatures <400K diffusion is essentially athermal and due to ballistic mixing. At temperatures between 400K and 700K the diffusion, which is considerably enhanced over the usual thermal values, has an Arrhenius behavior with an activation energy of 0.37 eV. At higher temperatures thermal diffusion, with an activation energy of 1.42 eV, dominates.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: A novel regime of crystal growth and segregation has been observed. Amorphous Si layers were uniformly doped with Au and epitaxial crystallization was induced in the temperature range 250–420°C using 2.5 MeV Ar ion irradiation. The Au segregation at the amorphous/crystal interface is analogous to behavior at liquid/solid interfaces except that the interfacial segregation coefficient of 0.007 at 320°C is independent of velocity between 0.6 and 6A/sec. This process results in the trapping of Au in crystalline Si at concentrations some ten orders of magnitude in excess of equilibrium concentration.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: Planar low-temperature solid phase epitaxy of amorphous silicon in a-Si/10nmNiSi/c-Si structure was observed. The crystallization rate is well described by the arrhenius-type expression with the activation energy and preexponencial factor deduced from our measurements of 1.7 eV and 2.4×1012 nm/min, respectively. NiSi2 formation at the NiSi2/a-Si interface is believed to be the limiting stage of the transformation. The structures with thicker Ni-reached interfacial layer perform much poorer a-Si epitaxy.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    M. Duan · J. Linnros · C. S. Petersson · K. V. Rao

    Full-text · Article · Jan 2011 · MRS Online Proceeding Library

  • No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • J. Linnros · R. G. Elliman · W. L. Brown
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    ABSTRACT: The transition from ion induced epitaxial crystallization to planar amorphization of a preexisting amorphous layer in silicon has been investigated. The conditions for dynamic equilibrium at the transition were determined for different ion species as a function of dose rate and temperature. The critical dose rate for equilibrium varies exponentially with 1/T, exhibiting an activation energy of approximately 1. 2 eV. Furthermore, for different ions, the critical dose rate is inversely proportional to the square of the linear displacement density created by individual ions. This second order defect production process and the activation energy, which is characteristic of divacancy dissociation, suggest that the accumulation of divacancies at the amorphous/crystalline interface controls the balance between crystallization and amorphization.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
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    ABSTRACT: The formation of NiSi and NiSi2 upon annealing of an ion-amorphized Ni/Si structure has been studied by various surface analytical techniques to characterize the morphology, stoichiometry and interface sharpness of the NiSi2 layer. In comparison with reactions of nickel on crystalline silicon (c-Si), sharpening 0ofthe NiSi2/C-Si interface is obtained for appropriate amorphization depths. Moreover, the surface roughness of the NiSi2 films is significantly reduced by implantation. The NiSi2 formation temperature is, however, not reduced as observed for structures with nickel deposited on amorphous silicon prepared by evaporation. This dissimilarity can be explained by an unexpected low crystallization temperature or the ion-amorphized structure, where Ni-ennanced solid phase epitaxy occurs at a temperature as low as 425°C.
    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • Robert Juhasz · Jan Linnros · Pascal Kleimann

    No preview · Article · Jan 2011 · MRS Online Proceeding Library
  • V. Grivickas · K. Gulbinas · G. Manolis · M. Kato · J. Linnros
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    ABSTRACT: Residual stress and carrier lifetime variation have been measured in free-standing n-type 3C-SiC wafer grown on undulated Si substrate. We identify extended regions of residual stress that lie parallel to epilayer surfaces. The opposite polarity of stress is identified toward the interface and toward the top surface. Integrated carrier lifetime has been determined by random defect density distribution which is enhanced in the areas of double-positioning boundary defects. It is shown that carrier lifetimes are severely reduced by the presence of residual stress towards epilayer surfaces. In this way lifetime depth-distribution can be mistakenly attributed to enhanced surface recombination.
    No preview · Article · Nov 2010
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    ABSTRACT: A 3D X-ray detector for imaging of 30–200 keV photons is described. It comprises a stack of semitransparent structured scintillators, where each scintillator is a regular array of waveguides in silicon, and with pores filled with CsI. The performance of the detector is described theoretically and explored in detail through simulations. The resolution of a single screen is shown to be determined only by the pitch, at least up to 100 keV. In comparison to conventional homogenous screens an improvement in efficiency by a factor 5–15 is obtainable. The cross-talk between screens in the 3D detector is shown to be negligible. The concept of such a 3D detector enables ray tracing and super resolution algorithms to be applied. Realized pore geometries have a lower aspect ratio than used in simulations and the roughness of the pore walls gives a 13% decrease in waveguide efficiency. Compared to currently used regular scintillators with similar resolution an efficiency increase by a factor 4 has been found for the structured scintillator.
    No preview · Article · Aug 2009 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: Two-photon absorption (TPA) in GaSe is detected in the narrow (about kT) spectral range above the indirect exciton energy for E⊥c light polarization. The appearance of TPA enhancement within narrow spectral region links to the resonant Raman scattering and anti-Stockes photoluminescence previously identified in GaSe. Extracted TPA coefficient is of the order of 10 cm/W and 5–10 times exceeds ones obtained previously for lower quanta energies.
    Full-text · Article · Mar 2008 · Journal of Physics Conference Series

Publication Stats

2k Citations
233.71 Total Impact Points

Institutions

  • 1992-2014
    • KTH Royal Institute of Technology
      • • Department of Microelectronics and Information Technology
      • • Department of Material- and Nano Physics
      • • Department of Microelectronics and Applied Physics (MAP)
      • • School of Information and Communication Technology (ICT)
      Tukholma, Stockholm, Sweden
  • 2003
    • Case Western Reserve University
      • Department of Materials Science and Engineering
      Cleveland, Ohio, United States
  • 2000-2001
    • Claude Bernard University Lyon 1
      Villeurbanne, Rhône-Alpes, France
  • 1982-1988
    • Chalmers University of Technology
      • Department of Applied Physics
      Goeteborg, Västra Götaland, Sweden