Browsing by Author "Shih, Y. T."

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Carrier Dynamics in Self-Assembled CdTe Stranski-Krastanow Quantum Dots Grown on ZnSe by Molecular Beam Epitaxy
(2008-11-01)
Yang, C. S.
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Chin, K. F.
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Lai, J. Y.
;
Luo, C. W.
;
Chou, W. C.
Self-assembled CdTe/ZnSe Stranski-Krastanow quantum-dot (QD) structures, which have a CdSe-like precursor-layer (PCL) between CdTe quantum dots and ZnSe matrix, were grown by molecular beam epitaxy. The carrier dynamics of the structures was studied by photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements. The temperature-dependent PL spectra revealed that there is a carrier transformation from small dots to larger dots via the precursor layer. Temperature-dependent PL measurements verify the existence of the QD excited excitonic state in 5.0 mono-layer (ML) coverage. In 0.6 ML coverage, the TRPL spectra exhibited a double-exponential decay process, as the detection energy at PCL emission energy. The faster decay time is corresponded to the carrier lifetime in PCL, the slower decay time exhibits the carrier in small QD. However, in 5.0 ML coverage, a faster and slower decay time represents the carrier lifetime in QD excited state for larger QD and the carrier lifetime in QD ground state for smaller QD.
Formation of a precursor layer in self-assembled CdTe quantum dots grown on ZnSe by molecular beam epitaxy
(2007-09-26)
Yang, C. S.
;
Wang, J. S.
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Lai, Y. J.
;
Luo, C. W.
;
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.
Quasi-Stranski-Krastanow growth mode of self-assembled CdTe quantum dots grown on ZnSe by molecular beam epitaxy
(2007-04-01)
Yang, C. S.
;
Lai, Y. J.
;
Chou, W. C.
;
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.