Browsing by Author "Lin, Kuo-Feng"

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Acoustic and optical phonon assisted formation of biexcitons
(2007-09-10)
Pan, Ching-Ju
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Lin, Kuo-Feng
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Hsieh, Wen-Feng
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光電工程學系
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Department of Photonics
Efficient exciton relaxation is required for bounding two cooled excitons to form biexciton. Acoustic and optical phonon scatterings playing key roles in exciton relaxation are responsible for formation of biexcitons at various temperatures. Using ZnO powders, the authors observed a sublinear dependence on excitation power at low temperature, in which the relaxation process involves only emission of acoustic phonons due to the excitons having kinetic energy lower than those of the optical phonons. However, the exponent comes near theoretical value of 2 for participation of optical phonons when the exciton kinetic energy approaches to the energy of the lowest optical phonon.
Bandgap engineering and spatial confinement of optical phonon in ZnO quantum dots
(2006-01-01)
Hsieh, Wen-Fen
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Lin, Kuo-Feng
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Cheng, Hsin-Ming
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Hsu, Hsu-Cheng
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光電工程學系
Upon decreasing size of ZnO quantum dots, the blueshift in bandgap reveals the quantum confinement effect and the diminishing ratio of the second- to first-order resonant Raman intensity reveals reducing the electron-phonon Frohlich interaction.
Calculations of electronic structure and density of states in the wurtzite structure of Zn(1) (-) (x)Mg(x)O alloys using sp(3) semi-empirical tight-binding model
(2009-01-01)
Lin, Kuo-Feng
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Pan, Ching-Ju
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Hsieh, Wen-Feng
;
光電工程學系
;
Department of Photonics
Calculating the electronic structure and the density of states in the wurtzite structure of Zn(1) (-) (x)Mg(x)O(ZMO) alloys using sp(3) semi-empirical tight-binding model, we observed increases of both band gap and electron effective mass that agree with the experimental results as increasing Mg composition up to x = 0.3. From the calculated total density of states, the increasing electron effective mass is a result of less orbital overlap of cation sites due to extra density of modes coming from Mg3s and Mg3p orbitals as introducing more Mg composition. Additionally, reducing electronegative characteristic of oxygen was caused by that the O2p was less localized around the oxygen atom.
Controlling electromagnetic wave through dual heights micro-lens array of a CMOS image sensor
(2016-05-15)
Lin, Kuo-Feng
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Hsiao, Yu-Kun
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Hsieh, Chin-Chuan
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Hsin, Shui-Chuan
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Hsieh, Wen-Feng
We demonstrate control of electromagnetic (EM) wave through dual heights micro-lens (DHML) array in 1.1 mu m pixel size complementary metal oxide semiconductor image sensor. The sensitivity and signal-to-noise ratio (SNR) are significantly improved ( > 10%) using the DHML structure. This DHML structure acts as an array of fundamental waveguides to enhance the optical throughput and to suppress the spatial crosstalk that is confirmed by evaluating the pixel performance in terms of the confinement factor of fundamental mode in this DHML structure. (C)) 2016 Published by Elsevier B.V.
Electronic structures and surface states of ZnO finite well structures
(2008-11-07)
Lin, Kuo-Feng
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Hsieh, Wen-Feng
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光電工程學系
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Department of Photonics
Electronic band structures and surface states were investigated for ZnO finite wells or slabs grown along < 0 0 0 1 > and < 1 - 1 0 0 > directions using tight-binding representation. The dangling bonds on two end-surfaces caused surface bands for different direction grown slabs, of which the wavefunctions tend to localize at the end-surfaces. The increasing splitting of the degenerate surface bands at the Gamma point was observed to decrease with the thickness of the nonpolar [1 - 1 0 0] slab. And the quantum confinement effect is distinctively enhanced by the extra electron field induced in the < 0 0 0 1 > grown finite well with the polar end-surfaces.
Electronic structures and surface states of ZnO finite well structures
(2009)
Lin, Kuo-Feng
;
Hsieh, Wen-Feng
;
光電工程學系
;
Department of Photonics
Electronic band structures and surface states were investigated for ZnO finite wells or slabs grown along < 0001 > and < 1-100 > directions using tight binding representation. The dangling bonds on two end-surfaces caused surface bands for different directions grown slabs, of which the wavefunctions tend to localize at the end surfaces. The increasing splitting of the degenerate surface bands at the Gamma point was observed decreasing with the thickness of the nonpolar [1-100] slab. And, the quantum confinement effect is distinctively enhanced by the extra electron-field induced in the < 0001 > grown finite well with the polar end-surfaces.
Phase retrieval by using the transport-of-intensity equation with Hilbert transform
(2016-04-01)
Li, Wei-Shuo
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Chen, Chun-Wei
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Lin, Kuo-Feng
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Chen, Hou-Ren
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Tsai, Chih-Ya
Phase recovery by solving the transport-of-intensity equation (TIE) is a non-iterative and non-interferometric phase retrieval technique. From solving the TIE with conventional, one partial derivative and Hilbert transform methods for both the periodic and aperiodic samples, we demonstrate that the Hilbert transform method can provide the smoother phase images with edge enhancement and fine structures. Furthermore, compared with the images measured by optical and atomic force microscopy, the Hilbert transform method has the ability to quantitatively map out the phase images for both the periodic and aperiodic structures. (C) 2016 Optical Society of America
Raman study of alloy potential fluctuations in MgxZn1-xO nanopowders
(2007-05-09)
Pan, Ching-Ju
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Lin, Kuo-Feng
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Hsu, Wei-Tse
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Hsieh, Wen-Feng
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光電工程學系
The blueshift of near-band-edge emission and excitonic absorption indicate that Zn2+ ions are successfully substituted by Mg2+ ions in MgxZn1-xO nanopowders for 0 <= x <= 0.14. The changes in Raman spectral linewidth and the asymmetry of the E-2 ( high) mode for various Mg contents can be well described by a modified spatial correlation model that considers the grain size distribution. With increasing Mg concentration, the alloy potential fluctuations lead to a decrease in the grain size, which is induced by the surplus Mg2+ that could form MgO clusters surrounding the crystalline MgZnO.
Reducing exciton-longitudinal optical phonon coupling with increasing Mg incorporation in MgZnO powders
(2007-12-15)
Pan, Ching-Ju
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Lin, Kuo-Feng
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Hsu, Wei-Tse
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Hsieh, Wen-Feng
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光電工程學系
The coupling between exciton and longitudinal optical (LO) phonon was investigated in the use of temperature-dependent photoluminescence from Mg(x)Zn(1-x)O powders prepared by a sol-gel method in the range of 0 <= x <= 0.05. The exciton binding energy increases to 73 meV for 5 at. % Mg incorporated powders. The strength of exciton-LO phonon coupling was deduced from the energy shift of exciton emission with temperature variation. The increase of the exciton binding energy results from a decrease of the exciton Bohr radius that is responsible for reducing the coupling strength of exciton-LO phonon as increasing Mg content. (c) 2007 American Institute of Physics.
Reducing exciton-longitudinal-optical phonon interaction with shrinking ZnO quantum dots
(2007-10-29)
Hsu, Wei-Tse
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Lin, Kuo-Feng
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Hsieh, Wen-Feng
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光電工程學系
;
Department of Photonics
The exciton-longitudinal-optical-phonon (LO-phonon) interaction was observed to decrease with reducing ZnO particle size to its exciton Bohr radius (a(B)). The unapparent LO-phonon replicas of free exciton (FX) emission and the smaller FX energy difference between 13 and 300 K reveal decreasing weighting of exciton-LO phonon coupling strength. The diminished Frohlich interaction mainly results from the reducing a(B) with size due to the quantum confinement effect that makes the exciton less polar. (C) 2007 American Institute of Physics.