Browsing by Author "Chien, Kun-Feng"

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Growth evolution and magneto-optical characteristics of self-assembled ZnTe/ZnMnSe quantum dots
(2013-09-01)
Lee, Ling
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Fan, Wen-Chung
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Chien, Kun-Feng
;
Tzou, An-Jye
;
Chou, Wu-Ching
The growth evolution and the magneto-optical characteristics of the self-assembled single-layer ZnTe/ZnMnSe quantum dots grown by molecular beam epitaxy were investigated. As the ZnTe coverage is above 2.0 monolayers, a Stranski-Krastanov growth process is observed with a significantly increased dot density on top of two-dimensional plateaus. As the coverage exceeds 2.7 monolayers, ripened dots dominate instead. Furthermore, a saturated degree of circular polarization of 76% at applied magnetic field of 4 T and the formation of magnetic polarons with a formation time of 7.4 ns were demonstrated. (c) 2012 Elsevier B.V. All rights reserved.
Improvement of defect reduction in semi-polar GaN grown on shallow-trenched Si(001) substrate
(2012)
Lee, Ling
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Chien, Kun-Feng
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Chou, Wu-Ching
;
Ko, Chih-Hsin
;
Wu, Cheng-Hsien
The improved design of sub-micron trenches on Si(001) substrate was demonstrated for defect suppression in semi-polar selectively-grown GaN layers. Cathodoluminescence and transmission electron microscopy measurements revealed a dramatically decreased density of threading dislocations and stacking faults near the surface of the overgrown GaN layer when the trench width ranged from 500 to 1500 nm. It was observed that defects were effectively trapped inside the trench when the ratio of trench depth to the SiO2 thickness is less than 0.66. In addition, a significant reduction of intrinsic polarization electric field was achieved for the InGaN/GaN multiple quantum well on the GaN selectively grown from the Si trenches.
Optical and Magnetic Properties of Zn1-xMnxO Grown by Plasma-Assisted Molecular Beam Epitaxy
(2014-06-01)
Chou, Wu Ching
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Tzou, An-Jye
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Chen, Hsuan-Shao
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Chien, Kun-Feng
;
Fan, Wen-Chung
Zn1-xMnxO films (0 <= x <= 0.070) were grown by plasma-assisted molecular beam epitaxy on Si substrates with AlN buffer layers. For low Mn concentration samples, x <= 0.02, photoluminescence spectra show strong near band edge emission. Strong phonon and exciton coupling-induced resonant Raman scattering was observed. Paramagnetic, antiferromagnetic, and ferromagnetic phases were observed. Room temperature ferromagnetism for all samples was attributed to the bound magnetic polaron effect.
Optical Studies of GaAs Nanowires Grown on Trenched Si(001) Substrate by Cathodoluminescence
(2012-06-01)
Lee, Ling
;
Chien, Kun-Feng
;
Fan, Wen-Chung
;
Chou, Wu-Ching
;
Ko, Chih-Hsin
"The strains in GaAs nanowires, which were grown from 1700- to 80-nm-wide trenches on the Si(001) wafer with SiO2 masks, were investigated by cathodoluminescence. For 1700- to 500-nm-wide trenches, the in-plane tensile strain at 15 K decreases with the decreasing trench width. The strain increases abruptly when the trench width is 300 nm, and then decreases as the trench width is further decreased. The results revealed that the stress induced by the SiO2 sidewalls dominates when the width is less than the depth of the trench. This approach provides an effective technique to measure the strain of a single nanowire and helps for the demonstration of selectively-grown GaAs with a designed strain. (C) 2012 The Japan Society of Applied Physics"