Browsing by Author "Yang, S. L."

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Admittance spectroscopy of the electric properties of 1,4-bis[N-(1-naphthyl)-N '-phenylamino]-4,4 ' diamine doped with tungsten oxide
(2006)
Hsieh, M. T.
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Chang, C. C.
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Hu, C. A.
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Huang, Y. T.
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Yang, S. L.
We report an efficient p-type doping of NPB layer using WO(3) as a p-dopant. We find that increasing the WO(3) volume percentage can reduce the activation energy of the NPB layer and increase the hole concentration in NPB layer. As a result, the hole-injection can be improved via tunneling through a narrow depletion region due to the increasing band bending which corresponds to the difference of Fermi level position between the ITO and the NPB layer.
Photonic band gap of two-dimensional triangular photonic crystals with broken structural and rotational symmetries
(2006-10-01)
Chang, K. P.
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Yang, S. L.
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電子物理學系
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Department of Electrophysics
Three deformed and two rotational structures are constructed to study the effect of structural and rotational symmetries on the gap widths of E- and H-polarization bands in photonic crystals. The band structures and field patterns of a triangular lattice of hollow tellurium (Te) rods are calculated using the plane-wave method. The H-polarization band gaps are strongly affected by the interaction between the fields of the rods as the rods are deformed and affected by the reduction in the rotational symmetry as whole rods are rotated. Only the shapes of the rods affect the E-polarization band gaps as the rods are either deformed or rotated. Moreover, H-polarization modes determine the absolute photonic band gap (PBG) width as the rods are rotated, whereas E-polarization modes determine the absolute PBG width as the rods are deformed. (c) 2006 American Institute of Physics.
Photonic band gaps of polygonal and circular dielectric rods in square lattices
(2008-12-01)
Chang, K. P.
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Yang, S. L.
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Shen, L. F.
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Yang, T. J.
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電子物理學系
The plane-wave method is employed to determine the band structures and the field patterns of the photonic crystals with polygonal and circular rods in square lattices. Isotropic and anisotropic N-fold polygonal rods are used to assess the effects of the shapes and symmetries of polygonal rods on E-and H-polarization modes. The photonic band structures of the polygonal rods approach those of the circular rods as N increases above a value that is determined by the optical properties of the photonic crystal. Moreover, for comparable geometric structures, anisotropic polygonal-rod photonic crystals can provide larger absolute photonic band gaps than isotropic photonic crystals. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3039213]
Pressure-dependent Raman scattering and photoluminescence of Zn1-xCdxSe epilayers
(2007-04-01)
Lin, Y. C.
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Chiu, C. H.
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Fan, W. C.
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Yang, S. L.
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Chuu, D. S.
Raman and photoluminescence spectra of cubic Zn1-xCdxSe (0 <= x <= 0.32) epilayers were obtained at high pressure. The impurity mode I observed in the phonon Raman spectra at low temperature confirms the intermediate phonon mode behavior. A split transverse optical phonon mode was found in the down-stroke high-pressure Raman scattering. Additionally, the pressure-dependent longitudinal optical (LO) phonon frequencies and the Gruneisen parameter (gamma(LO)) were obtained by quadratic polynomial fitting. Pressure-driven resonant Raman scattering effect was observed in samples with a high Cd concentration (x >= 0.18). The critical pressure of semiconductor-to-metal phase transition (Pt) decreases as the Cd content increases. As the Cd concentration increases from 0 to 0.32, Pt falls from 13.6 to 9.4 GPa, according to Pt (GPa)=13.6-6.8x-20.3x(2). (c) 2007 American Institute of Physics.
Pressure-induced metallization and resonant Raman scattering in Zn(1-x)Mn(x)Te
(2008-07-01)
Lin, Y. C.
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Fan, W. C.
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Chiu, C. H.
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Ke, F. K.
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Yang, S. L.
Pressure-induced resonant Raman scattering is adopted to analyze the zone-center optical phonon modes and crystal characteristics of Zn(1-x)Mn(x)Te (0 <= x <= 0.26) thin films. The pressure (Pt) at which the semiconducting undergoes a transition to the metallic phase declines as a function of Mn concentration (x) according to the formula Pt(x)=15.7-25.4x+19.0x(2) (GPa). Pressure-dependent longitudinal and transverse optical phonon frequencies and the calculated mode Gruneisen parameters were adopted to investigate the influence of Mn(2+) ions on the iconicity. The experimental results indicate that the manganese ions tend to increase the iconicity of ZnTe under ambient conditions, whereas an external hydrostatic pressure tends to reduce the iconicity and the bond length of Zn(1-x)Mn(x)Te. (c) 2008 American Institute of Physics.
Raman scattering of longitudinal-optical-phonon-plasmon coupling in Cl-doped ZnSe under high pressure
(2007-12-15)
Lin, Y. C.
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Chiu, C. H.
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Fan, W. C.
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Chia, C. H.
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Yang, S. L.
The vibrational, electronic, and crystalline properties of n-type chlorine-doped ZnSe (ZnSe:Cl) layers with a carrier concentration from 8.2x10(15) to 1.8x10(18) cm(-3) are studied by Raman spectroscopy. The spectral line shapes of the longitudinal-optical-phonon and plasmon coupling mode are analyzed using the Raman scattering efficiency and the dielectric function to obtain the electron densities and mobility. The splitting of the transverse-optical (TO) phonon and the redshift of the chlorine-related impurity vibration mode are clearly observed when pressure is applied. The semiconductor-to-metal phase transition pressure of ZnSe:Cl layers declines as the carrier concentration increases, indicating that n-type doping reduces crystal stability. Additionally, the pressure-induced weakening of the longitudinal-optical-phonon-plasmon coupling efficiency suggests that pressure tends to degrade the n-type characteristic of ZnSe:Cl because of the emergence of the new deep donorlike state. (c) 2007 American Institute of Physics.
Switchable tunneling mode for cylindrical photonic quantum well consisting of photonic crystals containing liquid crystal
(2013-06-15)
Hu, C. A.
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Yang, S. L.
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Yang, T. J.
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電子物理學系
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Department of Electrophysics
We propose a cylindrical photonic quantum well made of photonic crystals containing liquid crystals, the properties of which are theoretically calculated and investigated by the transfer matrix method in the cylindrical symmetry system. Liquid crystals are introduced into the photonic quantum well structure as tunable defect layers. When the liquid crystals are pseudo-isotropic state and the azimuthal mode order of incident waves are m=0, there were two pass-bands around certain wavelength. When the liquid crystals are homeotropic state, the reflectance of pass-band at shorter wavelength decreases from 0.75 to 0.05 in the TM mode, but the reflectance does not change in the TE mode. When mode order m=1 and the liquid crystals are pseudo-isotropic state, the reflectance of defect mode stayed the same as m=0. However, the result is reversed while the phase of liquid crystals change from pseudo-isotropic to homeotropic state. The reflectance is the same as in the TM mode, but that in the TE mode decreases substantially from 0.75 to 0.05. The application of our structure to switching device is highly potential. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.
Temperature dependence of excitonic emission in cubic CdSe thin film
(2008-01-01)
Chia, C. H.
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Yuan, C. T.
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Ku, J. T.
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Yang, S. L.
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Chou, W. C.
A detailed photoluminescence investigation of the thermal redshift and broadening of the excitonic line of cubic CdSe film grown by molecular beam epitaxy is presented. Free excitonic emission from the cubic Use film was observed at low temperature. Temperature-dependent measurement was performed to obtain material parameters related to exciton-phonon interaction by fitting the experimental data to the phenomenological model. The relative contribution of both acoustic and optical phonon to the band gap shrinkage and exciton linewidth broadening are discussed. Exciton binding energy of 16 +/- 1.5 meV was determined from the Arrhenius analysis. (C) 2007 Elsevier B.V. All rights reserved.
Time-resolved photoluminescence of isoelectronic traps in ZnSe(1-x)Te(x) semiconductor alloys
(2008-12-15)
Lin, Y. C.
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Chou, W. C.
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Fan, W. C.
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Ku, J. T.
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Ke, F. K.
Kohlrausch's stretched exponential law correlates well with the photoluminescence (PL) decay profiles of ZnSe(1-x)Te(x). As the Te concentration increases, the stretching exponent beta initially declines and then monotonically increases. This result can be understood using the hopping-transport and energy transfer model. The increase in the number of isoelectronic Te localized traps can reduce the PL decay rate and increase the linewidth, whereas the hybridization of the Te localized states with the valence-band edge states causes a reduction in both the lifetime and linewidth.
Time-resolved photoluminescence of isoelectronic traps in ZnSe1-xTex semiconductor alloys
(2008-12-15)
Lin, Y. C.
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Chou, W. C.
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Fan, W. C.
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Ku, J. T.
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Ke, F. K.
Kohlrausch's stretched exponential law correlates well with the photoluminescence (PL) decay profiles of ZnSe1-xTex. As the Te concentration increases, the stretching exponent beta initially declines and then monotonically increases. This result can be understood using the hopping-transport and energy transfer model. The increase in the number of isoelectronic Te localized traps can reduce the PL decay rate and increase the linewidth, whereas the hybridization of the Te localized states with the valence-band edge states causes a reduction in both the lifetime and linewidth.