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Träfflista för sökning "LAR1:liu ;pers:(Syväjärvi Mikael);pers:(Yakimova Rositza)"

Sökning: LAR1:liu > Syväjärvi Mikael > Yakimova Rositza

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1.
  • Eriksson, Jens, et al. (författare)
  • The influence of substrate morphology on thickness uniformity and unintentional doping of epitaxial graphene on SiC
  • 2012
  • Ingår i: Applied Physics Letters. - 0003-6951. ; 100:24, s. 241607
  • Tidskriftsartikel (refereegranskat)abstract
    • A pivotal issue for the fabrication of electronic devices on epitaxial graphene on SiC is controlling the number of layers and reducing localized thickness inhomogeneities. Of equal importance is to understand what governs the unintentional doping of the graphene from the substrate. The influence of substrate surface topography on these two issues was studied by work function measurements and local surface potential mapping. The carrier concentration and the uniformity of epitaxial graphene samples grown under identical conditions and on substrates of nominally identical orientation were both found to depend strongly on the terrace width of the SiC substrate after growth.
2.
  • Jokubavicius, Valdas, et al. (författare)
  • Effects of source material on epitaxial growth of fluorescent SiC
  • 2012
  • Ingår i: Thin Solid Films. - Elsevier. - 0040-6090. ; 522, s. 7-10
  • Tidskriftsartikel (refereegranskat)abstract
    • The growth of fluorescent SiC using Fast Sublimation Growth Process was demonstrated using different types of SiC source materials. These were prepared by (i) high-temperature hot pressing, (ii) chemical vapor deposition and (iii) physical vapor transport. The optimized growth rates of 50 μm/h, 170 μm/h and 200 μm/h were achieved using the three types of sources, respectively. The best results in respect to growth rates are obtained using higher density sources. Fluorescent SiC layers with mirror-like morphology, very good crystal quality and yellowish or warm white light photoluminescence at room temperature were grown using all three types of the source materials.
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3.
  • Jokubavicius, Valdas, et al. (författare)
  • Geometrical Control of 3C and 6H-SiC Nucleation on Low Off-Axis Substrates
  • 2011
  • Ingår i: Materials Science Forum. - 0255-5476. ; 679-680, s. 103-106
  • Tidskriftsartikel (refereegranskat)abstract
    • Growth of 3C or 6H-SiC epilayers on low off-axis 6H-SiC substrates can be mastered by changing the size of the on axis plane formed by long terraces in the epilayer using geometrical control. The desired polytype can be selected in thick (~200 µm) layers of both 6H-SiC and 3C-SiC polytypes on substrates with off-orientation as low as 1.4 and 2 degrees. The resultant crystal quality of the 3C and the 6H-SiC epilayers, grown under the same process parameters, deteriorates when lowering the off-orientation of the substrate.
4.
  • Jokubavicius, Valdas, et al. (författare)
  • On stabilization of 3C-SiC using low off-axis 6H-SiC substrates
  • 2012
  • Konferensbidrag (refereegranskat)abstract
    • Heteroepitaxial growth of 3C-SiC on 0.8 and 1.2 degree off-oriented 6H-SiC substrates was studied using a sublimation growth process. The 3C-SiC layers were grown at high growth rates with layer thickness up to 300 µm. The formation and the quality of 3C-SiC are influenced by the off-orientation of the substrate, the growth temperature (studied temperature range from 1750 oC to 1850oC), and the growth ambient (vacuum at 5*10-5 mbar and nitrogen at 5*10-1 mbar). The largest domains of 3C-SiC and the lowest number of double positioning boundaries were grown using nitrogen ambient and the highest growth temperature. The combined use of low off-axis substrate and high growth rate is a potential method to obtain material with bulk properties.
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5.
  • Ou, Yiyu, et al. (författare)
  • Characterization of donor–acceptor-pair emission in fluorescent 6H-SiC
  • 2012
  • Ingår i: Physica Scripta. - Institute of Physics Publishing Ltd. - 0031-8949. ; T148, s. 014003
  • Tidskriftsartikel (refereegranskat)abstract
    • We investigated donor–acceptor-pair emission in N–B-doped 6H-SiC samples by using photoluminescence (PL) and angle-resolved PL. It is shown that n-type doping with concentrations larger than 1018 cm−3 is favorable for observing luminescence, and increasing nitrogen results in stronger luminescence. A dopant concentration difference greater than 4×1018 cm−3 is proposed to help achieve intense PL. Angular-dependent PL was observed that was attributed to the Fabry–Pérot microcavity interference effect, and a strong luminescence intensity in a large emission angle range was also achieved. The results indicate that N–B-doped fluorescent SiC is a good wavelength converter in white LED applications.
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6.
  • Ou, Yiyu, et al. (författare)
  • Omnidirectional luminescence enhancement of fluorescent SiC via pseudoperiodic antireflective subwavelength structures
  • 2012
  • Ingår i: Optics Letters. - 0146-9592. ; 37:18, s. 3816-3818
  • Tidskriftsartikel (refereegranskat)abstract
    • In the present work, an approach of fabricating pseudoperiodic antireflective subwavelength structures (ARS) on fluorescent SiC by using self-assembled etch mask is demonstrated. By applying the pseudoperiodic (ARS), the average surface reflectance at 6° incidence over the spectral range of 390–785 nm is dramatically suppressed from 20.5% to 1.62%, and the hydrophobic surface with a large contact angle of 98° is also achieved. The angle-resolved photoluminescence study presents a considerable omnidirectional luminescence enhancement with an integral intensity enhancement of 66.3% and a fairly preserved spatial emission pattern.
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7.
  • Sun, Jianwu, et al. (författare)
  • Low Temperature Photoluminescence Signature of Stacking Faults in 6H-SiC Epilayers Grown on Low Angle Off-axis Substrates
  • 2012
  • Konferensbidrag (refereegranskat)abstract
    • The radiative recombination spectra of 6H-SiC epilayers grown on low angle (1.4° off-axis) substrates have been investigated by low temperature photoluminescence spectroscopy. Four different types of stacking faults have been identified, together with the presence of 3C-SiC inclusions. From the energy of the momentum-conserving phonons, four excitonic band gap energies have been found with Egx equal to 2.837, 2.698, 2.600 and 2.525 eV. These photoluminescence features, which give a rapid and non-destructive approach to identify stacking faults in 6H-SiC, provide a direct feedback to improve the material growth.
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8.
  • Vasiliauskas, Remigijus, et al. (författare)
  • Influence of twin boundary orientation on magnetoresistivity effect in free standing 3C–SiC
  • 2012
  • Ingår i: Materials letters (General ed.). - 0167-577X. ; 74, s. 203-205
  • Tidskriftsartikel (refereegranskat)abstract
    • Free standing 3C–SiC (111) samples with differently oriented twin boundaries were prepared using on-axis and slightly off-axis 6H–SiC substrates. The orientation of twin boundaries causes either an enhancement or suppression of the magnetoresistance mobility. The origin of carrier mobility difference is attributed to the specific structure of these defects. The height of the barriers created by twin boundaries was found to be 0.2 eV.
9.
  • Zoulis, G., et al. (författare)
  • Seeding layer influence on the low temperature photoluminescence intensity of 3C-SiC grown on 6H-SiC by sublimation epitaxy
  • 2012
  • Ingår i: HETEROSIC and WASMPE 2011. - Trans Tech Publications Inc.. ; s. 149-153
  • Konferensbidrag (refereegranskat)abstract
    • We report on n-type 3C-SiC samples grown by sublimation epitaxy. We focus on the low temperature photoluminescence intensity and show that the presence of a first conversion layer, grown at low temperature, is not only beneficial to improve the homogeneity of the polytype conversion but, also, to the LTPL signal intensity. From the use of a simple model, we show that this comes from a reduced density of non-radiative recombination centers.
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