Ho Suk Lee

Kyung Hee University, Sŏul, Seoul, South Korea

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Publications (8)14.44 Total impact

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    ABSTRACT: Spectroscopic ellipsometry was applied to study electro-optic effect in lead zirconate titanate^ (PZT) thin films grown epitaxially on Nb-doped SrTiO3(001) substrates by^ RF magnetron sputtering. Multilayer model analysis was applied^ to extract the ordinary and extraordinary refractive indices of the PZT thin film with electric^ field applied along the (001) direction. The effective linear and^ quadratic coefficients at a wavelength of 632.8 nm were estimated to be -134.6x10-12 m/V and 8.5x10-18 m^2/V^2, respectively, while the individual linear electro-optic^ coefficients r33 and r13 were -157.1 and 22 pm/V, respectively. We attributed existence of the linear electro-optic effect in unpoled PZT^ films to the presence of a built-in polarization^ and simultaneous poling during ellipsometric measurements.
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    ABSTRACT: Using spectroscopic ellipsometry electro-optic effect was studied in lead zirconate titanate (PZT) thin films grown epitaxially on Nb-doped SrTiO <sub>3</sub>(001) substrates by RF magnetron sputtering. A uniaxial multilayer model analysis was applied to extract the linear and quadratic electro-optic coefficients from the shifts in the ordinary and extraordinary refractive indices with electric field applied along the (001) direction. The effective linear and quadratic coefficients were measured as -134.6×10<sup>-12</sup> m / V and 8.5×10<sup>-18</sup> m <sup>2</sup>/ V <sup>2</sup> , respectively, at a wavelength of 632.8 nm, while the individual linear electro-optic coefficients r<sub>33</sub> and r<sub>13</sub> were -157.1 and 22 pm/V, respectively. The existence of the linear electro-optic effect in unpoled PZT films was attributed to the presence of a built-in polarization and simultaneous poling during measurements.
    Journal of Applied Physics 12/2008; 104(9-104):093103 - 093103-5. DOI:10.1063/1.3009655 · 2.19 Impact Factor
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    ABSTRACT: Amorphous GaInZnO and polycrystalline ZnO thin films are grown by rf magnetron sputtering. Their optical properties are investigated by spectroscopic ellipsometry. The optical gap of the GaInZnO film increases with the increase of Ga content and by annealing. These are attributed to the large band-gap energy of Ga2O3 and the structural relaxation after annealing, respectively. The changes in optical properties show a strong correlation to the device characteristics of GaInZnO thin film transistors: The turn-on voltage increases as the optical gap increases with increasing Ga/In ratio. This study shows that the GaInZnO thin films are as excellent as transparent oxide semiconductors.
    Applied Physics Letters 08/2007; 91(9):091910-091910-3. DOI:10.1063/1.2773952 · 3.52 Impact Factor
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    ABSTRACT: The purpose of this work is to investigate the effect of corona poling on the optical functions of the nonlinear-optical (NLO) polymers. We measured the complex refractive indices of NLO polymers deposited on glasses before and after corona poling using spectroscopic ellipsometry at room temperature at various incidence angles. In addition, we observed the absorption spectral change using ultraviolet-visible spectroscopy after corona poling, which is attributed to the chromophore orientation. In order to make NLO polymers, we attached a NLO active dye and photocrosslinkable moieties as side chains of poly(4-hydroxystyrene), deposited the polymer thin films on glass substrates by spin-coating, and corona-poled it along the surface-normal direction to align the dipoles of the chromophores along the electric field direction. In detail, PSDR1-25 designates a poly(4-hydroxystyrene) where 25% of hydroxyl groups in the side chain are substituted by disperse red 1 (DR1) and PSDR1-50 means the same except for 50% substitution. PSDR1 has the second-order NLO property, which is expected to show an acentric ordering by poling electric field. We used a parametric optical constant model to estimate the complex refractive index of the polymers. We found that the poling induced the uniaxial property of the complex refractive index of the polymers by aligning the chromophores along the poling direction. With increased poling voltage, we found that the oscillator strength of the major peak near the 2.4 eV (designated as E<sub>a</sub> ) peak decreases in the surface-parallel direction (x) , whereas that of the surface-normal direction (z) increases. Moreover, a detailed analysis of the dielectric functions using the standard critical point model showed that the poling induced a new peak E<sub>c</sub> (∼2.6 eV ) between dom- inant E<sub>a</sub> (∼2.3 eV ) and weak E<sub>b</sub> (∼2.9 eV ) peaks for PSDR1-50 polymers. With increased poling voltage, the E<sub>c</sub> peak strength increased compared to those of E<sub>a</sub> and E<sub>b</sub> peaks. We tentatively attribute E<sub>c</sub> to lower symmetry, possibly Stark effect, induced in the chromophores by the corona poling.
    Journal of Applied Physics 08/2007; 102(1-102):013514 - 013514-8. DOI:10.1063/1.2752116 · 2.19 Impact Factor
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    ABSTRACT: We grow Zn1−xMnxO/Al2O3 (0 ⩽ x ⩽ 0.08) thin films on sapphire (0001) using radio-frequency sputtering deposition method with Ar and various N2 flow rates. We examine the effect of N2 codoping on the band gap and Mn-related midgap absorption of (Zn,Mn)O. Using spectroscopic ellipsometry, we measure pseudodielectric functions in the spectral range between 1 and 4.5 eV. Using the model of Holden et al. [ T. Holden et al., Phys. Rev. B 56, 4037 (1997) ], we determine the uniaxial (Zn,Mn)O dielectric function and the E0 band-gap energy. The fitted band gap does not change appreciably with increasing Mn composition up to 2%. We find a very large broadening of both the E0 band gap and its exciton partner E0x peaks even for less than 2% of optically determined Mn composition. In ellipsometric spectra, we also find Mn-related 3 eV optical structure. In particular, optical absorption spectra with varying N2 gas flow rate show that the Mn-related peak intensity decreases with increasing N2 flux. The decrease of the 3 eV Mn-related peak intensity is attributed to increasing N2 flow rate and Mn–N hybridization.
    Journal of Applied Physics 06/2006; 99(11):113532-113532-5. DOI:10.1063/1.2202097 · 2.19 Impact Factor
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    ABSTRACT: We grow Zn1-xMnxO/Al2O3 (0
    Journal of Applied Physics 01/2006; 99. · 2.19 Impact Factor
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    ABSTRACT: We measured the pseudo-dielectric functions of several nonlinear optical (NLO) polymeric systems using spectroscopic ellipsometry in the spectral range between 0.8 and 4.7 eV . We fabricated the thin films after doping the nonlinear optical active chromophores into amorphous polycarbonate to show good optical transparency. We measured the ultraviolet-visible absorption spectra of the NLO chromophores in the film state. In order to determine the dielectric functions, we employed the Bruggeman effective medium approximation, assuming a mixture of two phases: host and guest. We used the Cauchy model for the dielectric function of the host polymer and a parametric optical constant model for that of the guest chromophore. We discussed the variation of the dielectric functions and the transition energies for various host-guest systems. In the gradient donor structural chromophores, we observed a decrease of the highest occupied molecular orbital (HOMO) lowest-unoccupied-molecular-orbital (LUMO) transition energy, and found a transition at about 3 eV . The decrease of HOMO—LUMO transition energy is attributed to the increase of electron donability and conjugative effect. We could fit the volume fractions of host and guest using spectroscopic ellipsometry, and compared them with the values estimated from the chemical structures of the molecules.
    Journal of Applied Physics 05/2005; 97(8-97):083543 - 083543-5. DOI:10.1063/1.1883727 · 2.19 Impact Factor

Publication Stats

33 Citations
14.44 Total Impact Points

Institutions

  • 2005–2008
    • Kyung Hee University
      • Department of Physics
      Sŏul, Seoul, South Korea