Browsing by Author "Lai, Y. J."

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Biexciton emission from sol-gel ZnMgO nanopowders
(2010-05-10)
Chia, C. H.
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Lai, Y. J.
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Hsu, W. L.
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Han, T. C.
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Chiou, J. W.
We studied the power-dependent photoluminescence of Zn(1-x)Mg(x)O nanopowders grown by sol-gel method, at temperature T = 100 K. At moderate optical pumping intensity, a nonlinear emission band due to the radiative recombination of free biexcitons was detected. We found that the free biexciton binding energies of Zn(1-x)Mg(x)O nanopowder (0.01 <= x <= 0.05) are nearly constant (13.5 +/- 1.5 meV). (C) 2010 American Institute of Physics. [doi:10.1063/1.3428780]
Effect of ZnSe partial capping on the ripening dynamics of CdSe quantum dots
(2007-02-19)
Lai, Y. J.
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Yang, C. S.
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Chen, W. K.
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Lee, M. C.
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Chang, W. H.
The ripening dynamics of CdSe quantum dots (QDs) partially capped with ZnSe layer are investigated. Atomic force microscopy (AFM) images show that the ripening of QDs is dramatically accelerated by depositing a ZnSe partial capping layer. The driving force of ripening enhancement is attributed to the increasing strain energy with capping thickness. For a ZnSe partial capping layer of below 3 ML, photoluminescence exhibits a clear redshift with increasing ZnSe monolayers. It is attributed to the size of the CdSe QD increases with ZnSe partial capping, in a manner that is consistent with the results of the AFM study. (c) 2007 American Institute of Physics.
Formation of a precursor layer in self-assembled CdTe quantum dots grown on ZnSe by molecular beam epitaxy
(2007-09-26)
Yang, C. S.
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Wang, J. S.
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Lai, Y. J.
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Luo, C. W.
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Chen, D. S.
The growth mode of CdTe quantum dots ( QDs) grown on highly lattice-mismatched ZnSe buffer was investigated. CdTe QDs ( 0.6 to 5.0 mono-layers ( MLs)) were deposited on the Se-stabilized ZnSe buffer layers using an alternating supply of Cd and Te atomic sources. Cross-sectional transmission electron microscopy and photoluminescence ( PL) measurements revealed the existence of a CdSe-like two-dimensional precursor layer ( PCL). The prominent difference in the temperature-dependent PL peak shift was associated with the emissions from the respective CdSe PCL and CdTe QDs. In addition, the PL excitation measurement demonstrated the existence of the first QD excited excitonic state.
High-excitation effect on photoluminescence of sol-gel ZnO nanopowder
(2010-02-22)
Chia, C. H.
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Lai, Y. J.
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Han, T. C.
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Chiou, J. W.
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Hu, Y. M.
We studied the power-dependent photoluminescence of ZnO nanopowder grown by sol-gel method at low temperature. At moderate optical pumping intensity, two nonlinear emission bands due to the radiative recombination of free biexciton and the inelastic exciton-exciton scattering were detected. We found that the threshold of the excitation density for the emergence of the nonlinear emission bands is low (< 18 W/cm(2)) in sol-gel ZnO nanopowders.
Quasi-Stranski-Krastanow growth mode of self-assembled CdTe quantum dots grown on ZnSe by molecular beam epitaxy
(2007-04-01)
Yang, C. S.
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Lai, Y. J.
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Chou, W. C.
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Chen, D. S.
;
Wang, J. S.
This study investigates the growth mode of highly lattice-mismatch (similar to 14%) CdTe self-assembled quantum dots grown on a ZnSe buffer-layer by molecular beam epitaxy. Two growth processes were used to prepare the samples. For the group-I samples, Te and Cd sources were alternately used to deposit a CdTe coverage layer of 0.6 to 8.0 mono-layers on a Zn-stabilized ZnSe buffer layer. The growth process of group-II samples was reversed; that is, the Cd beam was supplied first on a Se-stabilized ZnSe buffer layer. The optical spectra, including the power-dependent, time-resolved photoluminescence (PL) and PL excitation measurement, demonstrate a ZnTe-like and a CdSe-like two-dimensional precursor layer (wetting layer) in the group-I and group-II samples, respectively. Following the formation of the precursor layer, three-dimensional highly strained CdTe quantum dots were formed. Accordingly, the growth of CdTe self-assembled quantum-dot structures was attributed to the quasi-Stranski-Krastanow mode. (c) 2006 Elsevier B.V. All rights reserved.