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Time-resolved photoluminescence of isoelectronic traps in ZnSe1-xTex semiconductor alloys
(2008-12-15)
Lin, Y. C.
;
Chou, W. C.
;
Fan, W. C.
;
Ku, J. T.
;
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.
Lattice Dynamics and Crystalline Properties of Wurtzite Zn1-xMgxO Powders under High Pressure
(2011-10-13)
Lin, Y. C.
;
Tseng, C. L.
;
Chou, W. C.
;
Chia, C. H.
;
Han, T. C.
This investigation systematically studies the lattice dynamics and crystalline properties in Zn1-xMgxO using high-pressure Raman spectroscopy. The incorporation of Mg and the application of external pressure cause distinct phonon vibrational behaviors in ZnO. Accordingly, the 202.7, 332.7, and 511.5 cm(-1) phonons, which have been controversially assigned, can be conclusively identified. Detailed Raman spectra reveal that the metallic phase transition of ZnO is complete by around 13.2 GPa, which pressure is found to decrease as the Mg content increases. Upon pressure release, an unusual hysteresis effect (>10.0 GPa) in Zn1-xMgxO is observed. The degree of crystal ionicity and anisotropy importantly affects the phase transition pressure of Zn1-xMgxO. Under ambient conditions, ZnO becomes more ionic upon the incorporation of Mg and becomes more covalent under higher pressure. These results are caused by the interplay between the pressure dependence of the high-frequency dielectric constant and Born's transverse dynamical effective charge. The E-1-A(1) splitting of the longitudinal and transverse optical phonons is analyzed, yielding insight into the pressure-dependent crystal anisotropy of Zn1-xMgxO.
Growth and optical properties of ZnTe quantum dots on ZnMgSe by molecular beam epitaxy
(2015-09-01)
Fan, W. C.
;
Huang, S. H.
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Chou, W. C.
;
Tsou, M. H.
;
Yang, C. S.
Self-assembled type-II ZnTe quantum dots (QDs) were grown on GaAs (0 0 1) substrates with Zn1-xMgxSe (x=0.24 and 0.52) buffer layers by molecular beam epitaxy. The optical properties of ZnTe QDs were investigated by low-temperature photoluminescence (PL) and time-resolved PL. An abrupt variation of the PL peak energy with coverage implies the existence of wetting layer of 3.2 MLs and 40 MLs for the Mg concentration x=0.24 and 0.52, respectively. The thickness of wetting layer is larger than that of Zaire QDs grown on ZnSe buffer layers because the strain between ZaTe and Zn1-xMgxSe is smaller. The non-mono-exponential decay profiles reflect the processes of carrier transfer and recapture. The Kohlrausch\'s stretching exponential well fits the decay profiles of ZaTe/Zn1-xMgxSe QDs. (C) 2015 Elsevier B.V. All rights reserved.
Magneto-optical properties of ZnMnTe/ZnSe quantum dots
(2011-05-15)
Fan, W. C.
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Ku, J. T.
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Chou, W. C.
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Chen, W. K.
;
Chang, W. H.
The sigma(+) and sigma(-) circularly polarized time-integrated and time-resolved Photoluminescence (PL) measurements were employed to investigate the carrier spin dynamics of ZnMnTe/ZnSe Quantum Dots (QDs) grown on GaAs substrates by molecular beam epitaxy. The Kohlrausch's stretching exponential function well correlates both the sigma(+) and sigma(-) decay profiles. The measured spin relaxation time is about 23 ns. (C) 2010 Elsevier B.V. All rights reserved.
Preheating-temperature effect on structural and photoluminescent properties of sol-gel derived ZnO thin films
(2014-04-01)
Chia, C. H.
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Tsai, W. C.
;
Chou, W. C.
;
電子物理學系
;
Department of Electrophysics
We investigated he evolution of structural and low-temperature photoluminescence properties of sol-gel derived ZnO thin films, as a function of pre-heating temperature between 300 degrees C and 600 degrees C. The pre-heating crystallization plays an important role in the lineshape of PL spectra. The increase in pre-heating temperature enables rearrangement of atoms at the pre-heating stage, leading to c-axis oriented growth of films, modification in lineshape of impurity-detect emission, and reduction of deep-level emission intensity. (C) 2013 Elsevier B.V. All rights reserved
Thermal-activated carrier transfer in ZnCdO thin film grown by plasma-assisted molecular beam epitaxy
(2013-09-01)
Chien, K. F.
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Hsu, W. L.
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Tzou, A. J. .
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Lin, Y. C.
;
Chou, W. C.
` The thermal-activated carrier transfer processes in a Zn0.98Cd0.020 thin film grown by plasma-assisted molecular beam epitaxy were investigated using temperature-dependent and time-resolved photoluminescence (PL) spectroscopy. As the temperature increases from 50 to 220 K, the carriers transfer from shallow to deep localized states. Additionally, the carriers escape from the deep localized states above 220 K due to an activation energy of about 19 meV. (c) 2013 Elsevier B.V. All rights reserved.
Lattice Dynamics and Crystalline Properties of Wurtzite Zn(1-x)Mg(x)O Powders under High Pressure
(2011-10-13)
Lin, Y. C.
;
Tseng, C. L.
;
Chou, W. C.
;
Chia, C. H.
;
Han, T. C.
This investigation systematically studies the lattice dynamics and crystalline properties in Zn(1-x)Mg(x)O using high-pressure Raman spectroscopy. The incorporation of Mg and the application of external pressure cause distinct phonon vibrational behaviors in ZnO. Accordingly, the 202.7, 332.7, and 511.5 cm(-1) phonons, which have been controversially assigned, can be conclusively identified. Detailed Raman spectra reveal that the metallic phase transition of ZnO is complete by around 13.2 GPa, which pressure is found to decrease as the Mg content increases. Upon pressure release, an unusual hysteresis effect (>10.0 GPa) in Zn(1-x)Mg(x)O is observed. The degree of crystal ionicity and anisotropy importantly affects the phase transition pressure of Zn(1-x)Mg(x)O. Under ambient conditions, ZnO becomes more ionic upon the incorporation of Mg and becomes more covalent under higher pressure. These results are caused by the interplay between the pressure dependence of the high-frequency dielectric constant and Born's transverse dynamical effective charge. The E(1)-A(1) splitting of the longitudinal and transverse optical phonons is analyzed, yielding insight into the pressure-dependent crystal anisotropy of Zn(1-x)Mg(x)O.
Photoluminescence studies of type-II diluted magnetic semiconductor ZnMnTe/ZnSe quantum dots
(2006-12-25)
Kuo, M. C.
;
Hsu, J. S.
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Shen, J. L.
;
Chiu, K. C.
;
Fan, W. C.
Type-II diluted magnetic semiconductor ZnMnTe quantum dots (QDs) in ZnSe matrix grown by molecular beam epitaxy were investigated by conventional and magnetophotoluminescence (PL) spectroscopy. The QD emission exhibits a type-II characteristic in excitation power dependence of PL peak energy. A nonzero circular polarization of PL at the absence of magnetic field was observed. This phenomenon is attributed to the accumulation of interface charges confined in adjacent layers. The magneto-optical measurement demonstrates a magnetic-induced degree of circular polarization in the PL spectra, indicating the Mn incorporation into the QD system. (c) 2006 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.
;
Chia, C. H.
;
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.
Temperature dependence of excitonic emission in cubic CdSe thin film
(2008-01-01)
Chia, C. H.
;
Yuan, C. T.
;
Ku, J. T.
;
Yang, S. L.
;
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.

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