3.1 Estancias en cooperación internacional

URI permanente para esta colección

https://hdl.handle.net/20.500.12390/3674

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Examinando 3.1 Estancias en cooperación internacional por Autor "rp00710"
  • Publicación
    Band-fluctuations model for the fundamental absorption of crystalline and amorphous semiconductors: A dimensionless joint density of states analysis
    (Institute of Physics Publishing, 2019)
    Guerra Torres, Jorge Andrés
    ;
    Tejada A.
    ;
    Töfflinger J.A.
    ;
    Grieseler R.
    ;
    Korte L.
    We develop a band-fluctuations model which describes the absorption coefficient in the fundamental absorption region for direct and indirect electronic transitions in disordered semiconductor materials. The model accurately describes both the Urbach tail and absorption edge regions observed in such materials near the mobility edge in a single equation with only three fitting parameters. An asymptotic analysis leads to the universally observed exponential tail below the bandgap energy and to the absorption edge model at zero Kelvin above it, for either direct or indirect electronic transitions. The latter feature allows the discrimination between the absorption edge and absorption tails, thus yielding more accurate bandgap values when fitting optical absorption data. We examine the general character of the model using a dimensionless joint density of states formalism with a quantitative analysis of a large amount of optical absorption data. Both heavily doped p-type GaAs and nano-crystalline Ga 1-x Mn x N, as examples for direct bandgap materials, as well as amorphous Si:H x , SiC:H x and SiN x , are modeled successfully with this approach. We contrast our model with previously reported empirical models, showing in our case a suitable absorption coefficient shape capable of describing various distinct materials while also maintaining the universality of the exponential absorption tail and absorption edge. © 2019 IOP Publishing Ltd.
  • Publicación
    Combinatorial approach toward optimization of the light emission intensity of AlOxNy:Yb3+ thin films
    (Optica Publishing Group, 2019)
    Tucto, KY
    ;
    Aponte, W
    ;
    Dulanto, JA
    ;
    Tofflinger, JA
    ;
    Guerra, JA
    ;
    Grieseler, R
    To obtain an adequate luminescent emission, a significant effort must be made to find a suitable host material. An interesting and highly efficient method is a combinatorial approach, which allows high velocity screening of a wider range of properties. In the present work, a compositional gradient-based, thin-film library of 𝑎-AlOxNy:Yb3+ has been prepared by radio frequency co-sputtering from two targets. The ytterbium concentration range spreads from 0.9 to 4.2 at. % and the oxygen to nitrogen ratio from 0.6 to 3.6. Using different annealing temperatures, the activation energy of the rare earth ions and activation mechanisms can be evaluated. Finally, optimal elemental compositions in the investigated range are proposed.
  • Publicación
    Optical characterization and bandgap engineering of flat and wrinkle-textured FA(0.83)Cs(0.17)Pb(l(1-x)Brx)(3) perovskite thin films
    (AIP Publishing LLC., 2018)
    Tejada, A
    ;
    Braunger, S
    ;
    Korte, L
    ;
    Albrecht, S
    ;
    Rech, B
    ;
    Guerra, JA
    The complex refractive indices of formamidinium cesium lead mixed-halide [FA0.83Cs0.17Pb(I1– xBrx)3] perovskite thin films of compositions ranging from x = 0 to 0.4, with both flat and wrinkle-textured surface topographies, are reported. The films are characterized using a combination of variable angle spectroscopic ellipsometry and spectral transmittance in the wavelength range of 190 nm to 850 nm. Optical constants, film thicknesses and roughness layers are obtained point-by-point by minimizing a global error function, without using optical dispersion models, and including topographical information supplied by a laser confocal microscope.
  • Publicación
    Optical characterization and bandgap engineering of flat and wrinkle-textured FA0.83Cs0.17Pb(I1-xBrx)3 perovskite thin films
    (American Institute of Physics Inc., 2018)
    Tejada A.
    ;
    Braunger S.
    ;
    Korte L.
    ;
    Albrecht S.
    ;
    Rech B.
    ;
    Guerra J.A.
    The complex refractive indices of formamidinium cesium lead mixed-halide [FA0.83Cs0.17Pb(I1– xBrx)3] perovskite thin films of compositions ranging from x = 0 to 0.4, with both flat and wrinkle-textured surface topographies, are reported. The films are characterized using a combination of variable angle spectroscopic ellipsometry and spectral transmittance in the wavelength range of 190 nm to 850 nm.
  • Publicación
    The Urbach focus and optical properties of amorphous hydrogenated SiC thin films
    (IOP Publishing, 2016)
    Guerra, JA
    ;
    Angulo, JR
    ;
    Gomez, S
    ;
    Llamoza, J
    ;
    Montanez, LM
    ;
    Tejada, A
    ;
    Tofflinger, JA
    ;
    Winnacker, A
    ;
    Weingartner, R
    We report on the optical bandgap engineering of sputtered hydrogenated amorphous silicon carbide (a-SiC:H) thin films under different hydrogen dilution conditions during the deposition process and after post-deposition annealing treatments. The Tauc-gap and Urbach energy are calculated from ultraviolet-visible optical transmittance measurements. Additionally, the effect of the thermal annealing temperature on the hydrogen out-diffusion is assessed through infra-red absorption spectroscopy. A new model for the optical absorption of amorphous semiconductors is presented and employed to determine the bandgap as well as the Urbach energy from a single fit of the absorption coefficient. This model allowed the discrimination of the Urbach tail from the Tauc region without any external bias. Finally, the effect of the hydrogen dilution on the band-edge and the Urbach focus is discussed.