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🏛️國立陽明交通大學機構典藏

Access type: Metadata onlyAuthor: search.filters.author.Fan, W. C.

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Now showing 1 - 8 of 8
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    Coulomb induced recombination dynamics in magnetically doped type-IIb quantum dots
    (2019-01-01)
    Tarasek, S.
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    Chou, W-C.
    ;
    Fan, W. C.
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    Cartwright, A. N.
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    Thomay, T.
    We observe that the wavefunction overlap of the carriers in type-IIb quantum dots can be controlled by magnetic doping and strongly depends on the excitation power density. We study epitaxially grown ZnTe/ZnSe and magnetically doped (Zn,Mn)Te/ZnSe quantum dots that show a fast and slow recombination channel at two different energies. The emission shift of the slow recombination is independent of excitation power density (P-ex), whereas the fast recombination channel exhibits a larger emission shift with increasing P-ex. This blue shift saturates for high P-ex, however at a lower P-ex and smaller maximum shift in the magnetic system compared to the nonmagnetic system. The emission wavelength immediately after pulsed excitation typically changes as a function of charge carrier density due to the spatially indirect nature of type-IIb quantum dots. As carriers increase, the confinement potential of the system is altered due to a Coulomb interaction. The magnetic system exhibits a limited change in the wavefunction overlap of the carriers for high excitation power densities which we attribute to magnetic interactions to the hole wavefunction inside the dot. This would allow for an external manipulation of the magnetic polaron binding energy through varying the excitation power density P-ex in quantum dots.
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    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.
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    Optical characterization of isoelectronic ZnSe1-xOx semiconductors
    (2011-05-15)
    Lin, Y. C.
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    Chung, H. L.
    ;
    Ku, J. T.
    ;
    Chen, C. Y.
    ;
    Chien, K. F.
    We have studied the temperature dependence of the band gap and the decay dynamics of isoelectronic ZnSe1-xOx (x=0-0.053) semiconductors, using photoluminescence (PL) and time-resolved PL spectroscopy. The temperature dependence of the band gap of ZnSe1-xOx decreases with the increase in 0 concentration. The Kohlrausch law is in good agreement with the O-induced complex decay profiles. As temperature increases, the mechanism of carrier decay undergoes a complicated change from trapped to free excitons. These findings are consistent with the temperature dependence of the stretching exponent beta. (C) 2010 Elsevier B.V. All rights reserved.
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    Study of extending carrier lifetime in ZnTe quantum dots coupled with ZnCdSe quantum well
    (2018-03-01)
    Fan, W. C.
    ;
    Chou, W. C.
    ;
    Lee, J. D.
    ;
    Lee, Ling
    ;
    Nguyen Dang Phu
    We demonstrated the growth of a self-assembled type-II ZnTe/ZnSe quantum dot (QD) structure coupled with a type-I Zn0.88Cd0.12Se/ZnSe quantum well (QW) on the (001) GaAs substrate by molecular beam epitaxy (MBE). As the spacer thickness is less than 2 nm, the carrier lifetime increasing from 20 ns to nearly 200 ns was successfully achieved. By utilizing the time-resolved photoluminescence (TRPL) and PL with different excitation power, we identify the PL emission from the coupled QDs consisting of two recombination mechanisms. One is the recombination between electrons in ZnSe barrier and holes confined within ZnTe QDs, and the other is between electrons confined in Zn0.88Cd0.12Se QW and holes confined within ZnTe QDs. According to the band diagram and power-dependent PL, both of the two recombinations reveal the type-II transition. In addition, the second recombination mechanism dominates the whole carrier recombination as the spacer thickness is less than 2 nm. A significant extension of carrier lifetime by increasing the electron and hole separation is illustrated in a type-II ZnTe/ZnSe QD structure coupling with a type-I ZnCdSe/ZnSe QW. Current sample structure could be used to increase the quantum efficient of solar cell based on the II-VI compound semiconductors.
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    Growth and optical properties of ZnTe quantum dots on ZnMgSe by molecular beam epitaxy
    (2015-09-01)
    Fan, W. C.
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    Huang, S. H.
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    Chou, W. C.
    ;
    Tsou, M. H.
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    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.
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    Robust magnetic polarons in type-II (Zn, Mn) Te/ZnSe magnetic quantum dots
    (2010-11-18)
    Sellers, I. R.
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    Oszwaldowski, R.
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    Whiteside, V. R.
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    Eginligil, M.
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    Petrou, A.
    We present a magneto-optical study of magnetic polarons in type-II (Zn, Mn) Te quantum dots. The polarons are formed due to the exchange coupling between the spins of the holes and those of the Mn ions, both of which are localized in the dots. In our photoluminescence studies, the magnetic polarons are detected at temperatures up to similar to 150 K, with a formation energy of similar to 40 meV. The emission from these dots exhibits an unusually small Zeeman shift with applied magnetic field (similar to 2 meV at 8 T) and at the same time a very large circular polarization. We attribute this apparently contradictory behavior by a low and weakly temperature-dependent magnetic susceptibility due to antiferromagnetic coupling of the Mn spins.
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    Optical characterization of isoelectronic ZnSe(1-x)O(x) semiconductors
    (2011-05-15)
    Lin, Y. C.
    ;
    Chung, H. L.
    ;
    Ku, J. T.
    ;
    Chen, C. Y.
    ;
    Chien, K. F.
    We have studied the temperature dependence of the band gap and the decay dynamics of isoelectronic ZnSe(1-x)O(x) (x=0-0.053) semiconductors, using photoluminescence (PL) and time-resolved PL spectroscopy. The temperature dependence of the band gap of ZnSe(1-x)O(x) decreases with the increase in 0 concentration. The Kohlrausch law is in good agreement with the O-induced complex decay profiles. As temperature increases, the mechanism of carrier decay undergoes a complicated change from trapped to free excitons. These findings are consistent with the temperature dependence of the stretching exponent beta. (C) 2010 Elsevier B.V. All rights reserved.
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    Time-resolved photoluminescence of isoelectronic traps in ZnSe(1-x)Te(x) 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 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.