Browsing by Author "Chiu, K. C."

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Catalyst-free highly vertically aligned ZnO nanoneedle arrays grown by plasma-assisted molecular beam epitaxy
(2009-11-01)
Wang, J. S.
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Yang, C. S.
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Chen, P. I.
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Su, C. F.
;
Chen, W. J.
This work describes the growth of highly vertically aligned ZnO nanoneedle arrays on wafer-scale catalyst-free c-plane sapphire substrates by plasma-assisted molecular beam epitaxy under high Zn flux conditions. The photoluminescence spectrum of the as-grown samples reveals strong free exciton emissions and donor-bound exciton emissions with an excellent full width at half maximum (FWHM) of 1.4 meV. The field emission of highly vertically aligned ZnO nanoneedle arrays closely follows the Fowler-Nordheim theory. The turn-on electric field was about 5.9 V/A mu m with a field enhancement factor beta of around 793.
Effects of substrate temperature on properties of Alq3 amorphous layers prepared by vacuum deposition
(2006-01-01)
Chiu, K. C.
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Jian, Z. A.
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Luo, Y. Z.
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Chung, J. M.
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Tang, S. J.
In this report, various organic Alq3 amorphous layers are prepared by vacuum deposition at different substrate temperatures T-sub (from 30 to 180 degrees C). The surface morphology, structural information, electrical and optical properties of these as-deposited layers are investigated by atomic force microscopy, X-ray diffraction, J-E curves, and photoluminescence studies, respectively. Furthermore, a temperature dependence of dark electrical conductivity sigma(T) deduced from J-E curves of these organic amorphous layers is presented. Finally, effects from T-sub on the physical properties of these organic Alq3 amorphous layers are discussed and a model based on a thermal interconversion between Alq3 isomers is proposed to explain these experimental results.
Influence of Zn/O flux ratio and Mn-doped ZnO buffer on the plasma-assisted molecular beam epitaxy of ZnO on c-plane sapphire
(2008-10-15)
Wang, J. S.
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Yang, C. S.
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Liou, M. J.
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Wu, C. X.
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Chiu, K. C.
This work investigated the influence of Zn/O flux ratio and Mn-doped ZnO buffer layer on the epitaxial growth of ZnO grown by plasma-assisted molecular beam epitaxy on c-plane sapphire substrates. Atomic force microscopy (AFM), photoluminescence (PL) and X-ray diffraction (XRD) measurements indicated that a small amount residual strain of ZnO epilayers was further relaxed under stoichiometric growth conditions due to the better surface migration of the adatoms. Moreover, we observed that a small amount of Mn doping led to obtain a flatter surface with stronger lattice relaxation maybe due to the greatly enhanced surface migration of the adatoms. By adding a Mn-doped ZnO buffer layer the optical and electrical properties of the ZnO epilayers had significant improvement. (c) 2008 Elsevier B.V. All rights reserved.
Photoluminescence studies of type-II diluted magnetic semiconductor ZnMnTe/ZnSe quantum dots
(2006-12-25)
Kuo, M. C.
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Hsu, J. S.
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Shen, J. L.
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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.
Temperature dependence of excitonic emission in cubic CdSe thin film
(2008-01-01)
Chia, C. H.
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Yuan, C. T.
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Ku, J. T.
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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.