Browsing by Author "Kuo, C. H."

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Characterization of n-GaN with Naturally Textured Surface for Photoelectrochemical Hydrogen Generation
(2010)
Liu, Shu-Yen
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Sheu, J. K.
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Ye, Jhao-Cheng
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Tu, S. J.
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Hsu, Che-Kang
To reduce light reflection and enlarge the effective reaction surface area at the n-GaN/electrolyte interface, n-GaN epitaxial layers with naturally textured surface are utilized. The layers are combined with Cr/Au ohmic contacts on n-GaN to form working electrodes that generate hydrogen by direct photoelectrolysis of water. Although the surface reflection on the naturally textured n-GaN samples is lower than that on n-GaN epitaxial layers with flat surface, our results reveal that the photocurrent (I(ph)) and gas generation rates (R(gas)) obtained from the naturally rough n-GaN samples are lower than those from the flat samples. The results can be attributed to the fact that the rough n-GaN surface caused by dense surface pits leads to significant recombination of photogenerated carriers with charged defects; this occurs before carriers reach the ohmic contacts, thereby resulting in lower I(ph) and R(gas). Related analyses have been performed and presented in this paper to initially explain the possible mechanism. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3499327] All rights reserved.
Characterization study of GaN-based epitaxial layer and light-emitting diode on nature-patterned sapphire substrate
(2012-03-01)
Lin, H. Y.
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Chen, Y. J.
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Chang, C. L.
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Li, X. F.
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Kuo, C. H.
Chemical wet etching on c-plane sapphire wafers by three etching solutions (H3PO4, H2SO4, and H3PO4/H2SO4 mixing solution) was studied. Among these etching agents, the mixing H3PO4/H2SO4 solution has the fastest etching rate (1.5 mu m/min). Interestingly, we found that H2SO4 does not etch the c-plane sapphire wafer in thickness; instead, a facet pyramidal pattern is formed on the c-plane sapphire wafer. GaN light-emitting diode (LED) epitaxial structure was grown on the sapphire wafer with the pyramidal pattern and the standard flat sapphire wafer. X-ray diffraction and photoluminescence measurement show that the pyramidal pattern on the sapphire wafer improved crystalline quality but augmented the compressive stress level in the GaN LED epilayer. The horizontal LED chips fabricated on the pyramidal-patterned sapphire wafer have a larger light output than the horizontal LED chips fabricated on the standard flat sapphire wafer by 20%.
Design and Applications of the Synchronized Motion Controller for Tapping Processes
(2012)
Yeh, C. F.
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Huang, W. S.
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Kuo, C. H.
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Hsu, P. L.
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電子工程學系及電子研究所
In this paper, linear and nonlinear control design techniques including: (1) cross-couple control, (2) nonlinear friction compensation, and (3) disturbance observer are suitably integrated to improve control performance in synchronization. The developed controller has been applied to a two-axis motion system with an induction motor and a servo motor, in which they have very different dynamic characteristics. Experimental results indicate that the maximum synchronized error is significantly reduced from 132.1 um to 4.3 um. Moreover, the positional type cross-coupled controller has been realized on a commercial CNC tapping machine to improve the maximum synchronized error. Results of the tapping process have led to synchronization accuracy under 10 um when the spindle speed increases to the CNC maximum speed 6000 rpm to maintain satisfactory tapping processes.
Displacement Coefficient Method for Bridge subjected to Pulse-Like Ground Motions
(2018-01-01)
Liu, K. Y.
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Wang, S. T.
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Hwang, C. C.
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Kuo, C. H.
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交大名義發表
This paper proposes the displacement coefficient, R-d, for bridge column subjected to near-fault earthquake. R-d is defined as a ratio between ultimate displacement and elastic displacement. 142 pulse-like ground motions are utilized to perform the nonlinear time history analysis with constant ductility from 1 to 6. This study investigates the R-d in four aspects, including (1) signal processing method, (2) orientation of the velocity, (3) hysteretic models, and (4) number of the ground motions. The analytical results are compared with the regulations specified in AASHTO 2011. For a structure with typical displacement ductility of 4, compared to the analytical results, the R-d in AASHTO 2011 is overestimated within the period of 0.5 second, and underestimated between 0.5 and 4 second. Therefore, the revised formulation of R-d is proposed, which could be suitable for the bridge considering the near-fault effect in Taiwan.
Effect of Fe2O3 coating on ZnO nanowires in photoelectrochemical water splitting: A synchrotron x-ray spectroscopic and spectromicroscopic investigation
(2020-06-01)
Lu, Y. R.
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Wang, Y. F.
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Chang, H. W.
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Huang, Y. C.
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Chen, J. L.
An array of ZnO/Fe2O3 core-shell nanowires (NW) for the highly efficient absorption of light and carrier collection is developed for use in photoelectrochemical (PEC) water-splitting. The oriented NW architecture favors physical matching, providing a direct electron conduction pathway and reducing the diffusion length of photogenerated holes. This work involves a combination of spectral imaging, spectromicroscopy and in situ x-ray absorption spectroscopy; spectra are obtained under operando conditions. Direct investigation of oriented nanowires using polarization-dependent x-ray spectromicroscopy enables the determination of the relationship between anisotropic electronic orbitals and charge carrier water-splitting efficiency. The results of O K-edge STXM demonstrated that the ZnO/Fe2O3 core-shell NW exhibits strong anisotropy and thus provides higher electron-hole transport efficiency than bare ZnO. In situ XAS revealed that interfacial charge transfer between Fe 3d and Zn 4p states enhances the photoelectrochemical reaction in the ZnO/Fe2O3 core-shell NW. The photogenerated electrons of Fe2O3 are transferred from Fe 3d states to the Zn 4p state under photoelectrochemical conditions.
Efficiency Improvement of GaN-Based Light-Emitting Diode Prepared on GaN Nanorod Template
(2010-02-15)
Kuo, C. H.
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Chang, L. C.
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Kuo, C. W.
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Chi, G. C.
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光電工程學系
We demonstrated the formation of GaN-based nanorod (NR) structure by using self-assemble Ni nanoislands as the etching mask. It was found that crystal quality of the GaN epilayer prepared on an NR GaN template was significantly better than that prepared with a conventional low-temperature GaN nucleation layer. With the NR GaN template, it was found that 20-mA light-emitting diode (LED) output power can be enhanced by 39.8%, as compared to the conventional LED.
Improved Power Conversion Efficiency of InGaN Photovoltaic Devices Grown on Patterned Sapphire Substrates
(2011-04-01)
Yang, C. C.
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Sheu, J. K.
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Kuo, C. H.
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Huang, M. S.
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Tu, S. J.
The InGaN/sapphire-based photovoltaic (PV) cells with Al(0.14)Ga(0.86)N/In(0.21)Ga(0.79)N superlattice structures that serve as absorption layers were grown on patterned sapphire substrates (PSSs). Under global air-mass 1.5 conditions, the short-circuit current density, the open-circuit voltage, and the fill factor obtained from the PV cells were 1.21 mA/cm(2), 2.18 V, and 0.65, respectively, corresponding to a conversion efficiency of 1.71%. Compared with PV devices grown on flat sapphire substrates, the photocurrent of PSS-grown PV devices was enhanced by 26%. The improved PV performance was attributable to the positive effects of the PSS on the material quality.
Interruption-free growth of 10 mu m-thick GaN film prepared on sputtered AlN/PSS template by hydride vapor phase epitaxy
(2015-09-15)
Chen, Y. A.
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Kuo, C. H.
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Wu, J. P.
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Chang, C. W.
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照明與能源光電研究所
GaN films (10 mu m-thick) of high crystalline quality were prepared on sputtered AlN/PSS template by hydride vapor phase epitaxy (HVPE). By introducing the two-step growth method into HVPE, one can reduce the steps in the procedure, realize uninterrupted growth, and improve the crystal quality of the films. The effects of initial GaN growth on the AlN/PSS template by HVPE were also investigated. In this study, 10 mu m-thick GaN films prepared on sputtered AlN/PSS template by HVPE showed improved crystal quality using X-ray diffraction and etching pits density. Compared with conventional undoped GaN film grown by metal organic chemical vapor deposition, the full width at half maximum of the (0 0 2) and (1 0 2) peaks of GaN decreased from 450 arcsec to 290 arcsec and from 376 arcsec to 344 arcsec, respectively. Transmission electron microscopy results showed that the gaps observed between the convex regions would eventually turn into dislocations during coalescence, because the number of dislocations increased with the number of gaps observed between the convex regions after step-1 growth. (C) 2015 Elsevier B.V. All rights reserved
Nonpolar light emitting diode made by m-plane n-ZnO/p-GaN heterostructure
(2011-12-01)
Chen, C. W.
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Hung, S. C.
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Lee, C. H.
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Tun, C. J.
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Kuo, C. H.
Nonpolar (100) m-plane n-ZnO/p-GaN light-emitting-diodes (LEDs) were grown by chemical vapor deposition on p-GaN templates which was grown by metalorganic chemical vapor deposition on LiAlO(2)(100) substrate. Direct current (DC) electroluminescence (EL) measurements yielded a peak at 458nm. The EL peak position was independent of drive current and a full width of half maximum (FWHM) of 21.8 nm was realized at 20mA. The current-voltage characteristics of these diodes showed a forward voltage (V(f)) of 6V with a series resistance of 2.2 x 10(5) Omega. (C) 2011 Optical Society of America
Single Crystalline GaN Epitaxial Layer Prepared on Nano-Patterned Si(001) Substrate
(2011)
Huang, C. C.
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Chang, S. J.
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Kuo, C. H.
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Wu, C. H.
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Ko, C. H.
The authors report the growth of GaN epitaxial layers on nano-patterned Si(001) substrates prepared by the standard facilities used in integrated circuit (IC) industry. It was found that we could achieve high-quality single crystalline GaN by using the 50 nm SiO(2) recess patterned Si(001) substrate. It was also found that we can reduce the tensile stress in GaN epitaxial layer by about 95% using the nano-patterned Si(001) substrate, as compared to the conventional un-patterned Si(111) substrate. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3569753] All rights reserved.