Browsing by Author "Chang, H. J."

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Optical properties of InGaN quantum dots grown by SiN(x) nanomasks
(2007-04-15)
Huang, L. L.
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Chang, H. J.
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Chou, Y. Y.
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Wang, C. H.
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Chen, T. T.
InGaN quantum dots (QDs) deposited on SiN(x) nanomasks have been investigated by atomic force microscopy, photoluminescence (PL), and photoluminescence excitation (PLE) measurements. It was found that the size of QDs can be well controlled by SiN(x) nanomasks, enabling the manipulation of quantum confinement effect. The PL spectra of InGaN QDs contain several fine structures, and the main peaks can be attributed to families of QDs with different sizes. The emission arising from InGaN QDs and GaN buffer layer can be clearly distinguished based on PLE measurement, which can be used to improve the interpretation in the previous reports. Our study indicates that the quantum confined Stark effect due to piezoelectric field plays a very important role in the optical properties of InGaN QDs, which is very useful for the application of optoelectronic devices.(c) 2007 American Institute of Physics.
Optically modulated internal strain in InGaN quantum dots grown on SiNx nano masks
(2008-01-21)
Chang, H. J.
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Chen, T. T.
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Huang, L. L.
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Chen, Y. F.
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Tsai, J. Y.
Optically modulated internal strain has been observed in InGaN quantum dots (QDs) deposited on SiNx nano masks. The modulated internal strain can induce a number of intriguing effects, including the change of refractive index and the redshift of InGaN A(1)(LO) phonon. The underlying mechanism can be well accounted for in terms of the variation of internal strain through the converse piezoelectric effect arising from the screening of the internal electric field due to spatial separation of photoexcited electrons and holes. Our results point out a convenient way for the fine tuning of physical properties in nitride-based semiconductor nanostructures, which is very important for high quality optoelectronic devices. (c) 2006 Optical Society of America.
Suppression of Octahedral Tilts and Associated Changes in Electronic Properties at Epitaxial Oxide Heterostructure Interfaces
(2010-08-19)
Borisevich, A. Y.
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Chang, H. J.
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Huijben, M.
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Oxley, M. P.
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Okamoto, S.
Epitaxial oxide interfaces with broken translational symmetry have emerged as a central paradigm behind the novel behaviors of oxide superlattices. Here, we use scanning transmission electron microscopy to demonstrate a direct, quantitative unit-cell-by-unit-cell mapping of lattice parameters and oxygen octahedral rotations across the BiFeO(3)-La(0.7)Sr(0.3)MnO(3) interface to elucidate how the change of crystal symmetry is accommodated. Combined with low-loss electron energy loss spectroscopy imaging, we demonstrate a mesoscopic antiferrodistortive phase transition near the interface in BiFeO(3) and elucidate associated changes in electronic properties in a thin layer directly adjacent to the interface.