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Featured researches published by long Chen.


Semiconductor Science and Technology | 2014

Optical characteristics of nonpolar a-plane ZnO thin film on (010) LiGaO2 substrate

D. R. Hang; Sk Emdadul Islam; Krishna Hari Sharma; Chenlong Chen; Chi-Te Liang; Mitch M.C. Chou

We investigate the optical properties of non-polar a-plane ZnO film grown on (010) LiGaO2 substrate by chemical vapor deposition. X-ray diffraction indicates the a-plane orientation and Raman spectroscopy reveals the phase purity. Four distinct features in the near band-edge range are identified as neutral-donor-bound-exciton (D°X), free-exciton (FX), free-to-bound, and donor-acceptor pair transitions. The thermal activation energy of D°X is 12 meV while an acceptor energy level of 124 meV is estimated. Temperature evolution of photoluminescence (PL) shows that the room-temperature luminescence is a mixture of free-to-bound and FX transitions. The polarization dependence of the near-band-edge transitions were investigated. The largest degree of polarization of 95.5% occurs in FX transition. It can be attributed to anisotropic in-plane strain and the nonpolar a-plane orientation.


Journal of Applied Physics | 2010

Improved quality of nonpolar m-plane GaN [101¯0] on LiAlO2 substrate using a modified chemical vapor deposition

Mitch M.C. Chou; D. R. Hang; Liuwen Chang; Chenlong Chen; Wen-Fu Yang; Chu-An Li; Jih-Jen Wu

Nonpolar GaN crystal on lattice-matched [100] γ-LiAlO2 substrate was grown by a newly designed chemical vapor deposition (CVD) reactor. Following the CVD growth, x-ray diffraction indicated that the GaN film was oriented in the nonpolar m-plane with [101¯0] orientation. Further structural characterizations and defect analysis of nonpolar GaN material was performed using transmission electron microscope. Low-temperature photoluminescence was dominated by neutral donor bound excitons and the yellow luminescence was negligible. Raman spectroscopy showed that the as-grown GaN {101¯0} epilayer on [100] γ-LiAlO2 substrate were indeed of good quality. Compared to the previous report, nonpolar GaN with an improved quality was demonstrated by modifying the inner structure of the CVD reactor.


RSC Advances | 2015

Microstructural and optical properties of high-quality ZnO epitaxially grown on a LiGaO2 substrate

Chenlong Chen; Tao Yan; Shih-Hsun Yu; Chun-Yu Lee; Chi-Wei Chang; Mitch M.C. Chou

High-quality ZnO films have been reproducibly grown on a LiGaO2 substrate by chemical vapor deposition with optimized growth parameters. The in-plane epitaxial relationship of ZnO[100]//LiGaO2[100] is revealed by transmission electron microscopy (TEM). The surface morphology of as-grown ZnO films characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrates a very smooth surface with a root-mean-square roughness of 0.6 nm. The full width at half maximum value (FWHM) of 0.03° for the (0002) X-ray rocking curve shows the excellent crystalline quality of as-grown ZnO films. High transparency of the ZnO films in the visible range was revealed by optical transmittance measurements. The strong near-band-edge UV emission accompanied by a negligible defect-related green band emission suggests that the as-grown ZnO films have a high optical quality. Microstructural properties and strain state of the samples were also studied by TEM, X-ray diffraction (XRD) reciprocal space maps and Raman scattering analysis. Substrate compliant deformation, confirmed by the high-resolution TEM analysis, is suggested to be beneficial to decrease the compressive strain in the epilayer and increase the quality of the ZnO. This facile growth process towards high-quality ZnO opens up a broad potential application of high-efficiency ZnO-based devices on a LiGaO2 substrate.


Applied Physics Express | 2014

Resonant Raman scattering and photoluminescent properties of nonpolar a-plane ZnO thin film on LiGaO2 substrate

D. R. Hang; Krishna Hari Sharma; Sk Emdadul Islam; Chenlong Chen; Mitch M.C. Chou

Nonpolar a-plane ZnO thin films are grown on LiGaO2 substrates and their optical and vibronic characteristics are investigated. Raman spectroscopy under nonresonant and resonant excitations shows the phase purity and resonant multiphonon process. From multiphonon Raman peaks up to the 6th order in the resonant spectra, the LO phonon frequencies for wave vectors away from the Γ point are estimated using the cascade model. Polar LO phonons with E1 symmetry play an important role in the indirect transitions of hot excitons. The optical anisotropy has been studied on the basis of polarization-dependent photoluminescence. The origin of photoluminescence is studied and a donor binding energy of 74.6 meV is found.


Conference Proceedings Power Industry Computer Application Conference | 1993

Data extraction from a geographic information system for power system applications

M.T. Tsay; C.N. Lu; Whei-Min Lin; Chenlong Chen

This paper presents a preliminary design of an automated mapping/facilities management (AM/FM) system based on an integrated geographic information system (GIS). The GIS provides an environment for building an electric facilities database which includes graphic information and facility attribute data. The database can be used for engineering analysis, accounting and map production. Facility and network data can be retrieved by searching through the graphic and nongraphic data files. The retrieved data can then be used to form input data files for power system applications. With the powerful graphic capability of the system, simulation results can be viewed from the computer screen along with the graphic displays. In this paper, the integration of the GIS database and application software is illustrated by using a three-phase load flow program. The structure of the GIS database is introduced, and the interface programs are described. It is also shown that with the aid of GIS the facility statistic reports on system facilities can be easily established.<<ETX>>


International Journal of Electrical Power & Energy Systems | 1993

Integration of automatic mapping/facility management in distribution system analysis

M.T. Tsay; Whei-Min Lin; C.N. Lu; Chenlong Chen

Abstract This paper presents the use of an Automatic Mapping/Facility Management (AM/FM) system for distribution system analysis and design. The AM/FM provides an environment for building a database which contains both graphic information and non-graphic facility data. This database can be used by various departments for engineering analysis, accounting, inventory, map production, and so forth. This system can be used to retrieve facility data from the database and support different applications such as system analysis or planning. With the state-of-the-art graphic user interface (GUI), output results of the application can be shown on the screen along with the graphic displays of the system that includes the geographic information. In this paper, the integration of the AM/FM is illustrated by a three-phase load flow program, that is, a very precise and sophisticated three-phase distribution system model was used. It is also shown that a statistical report of facilities can be easily built with the aid of the AM/FM.


Journal of Rare Earths | 2012

Optical and thermoluminescence properties of Lu2Si2O7:Pr single crystal

He Feng; Guohao Ren; Yuntao Wu; Xu Jun; Qiuhong Yang; Jianjun Xie; Mitch M.C. Chou; Chenlong Chen

Single crystal of Lu2Si2O7:Pr was grown by Czochralski method. Transmittance, photoluminescence excitation (PLE) and photo- luminescence (PL) spectra, X-ray excited luminescence (XEL) and fluorescence decay time spectra of the sample were measured and dis- cussed to investigate its optical characteristics. The crystal structure of the as grown Lu2Si2O7:Pr was confirmed to be C2/m. There was a broad absorption peaking at 245 nm in the region from 200-260 nm. The PL spectrum was dominated by fast 3 PJ� 3 HJ band peaking at 524 nm. The XEL spectrum was dominated by the fast 5d 1 4f 1 �4f 2 emission peaking at 265 nm. The 2D (temperature-intensity) and 3D (tem- perature-wavelength-intensity) thermally stimulated luminescence (TSL) spectra were measured. The Pr 3+ ion was found to be the recombina- tion center during the TSL process. Three obvious traps were detected in LPS:Pr single crystal with energy depth at 1.06, 0.78 and 0.67 eV.


International Journal of Electrical Power & Energy Systems | 1992

A comparison of two heuristic approaches for distribution feeder switching contingencies

J.S. Wu; Chung-Nan Lee; Chenlong Chen; Kevin Tomsovic

Abstract In this paper, a comprehensive comparison of two distinct heuristic search approaches to solve the distribution switching problem is presented. One approach is based on a priority list of switches of the main search path defined by the feeder tie switch upstream to the substation. The other approach uses evaluation functions to address the problem. Evaluation functions are defined based on feeder layout, load level, and abnormal condition of the system to guide the searching process. A practical distribution system is used to test these two approaches. Items discussed include computing time, number of switching operations, and indices for feeder load balancing, transformer load balancing, and three-phase current balancing of their solutions. Results indicate that the priority list approach exhibits very high efficiency and solutions are fairly reliable. The evaluation function approach is more likely to find a solution with a minimum number of switching operations. Furthermore, the evaluation function approach is more robust in the case of serious contingencies.


Crystal Growth & Design | 2009

Crystal Growth of Nonpolar m-Plane ZnO on a Lattice-Matched (100) γ-LiAlO2 Substrate

Mitch M.C. Chou; Liuwen Chang; D. R. Hang; Chenlong Chen; Da-Sin Chang; Chu-An Li


Thin Solid Films | 2011

Epitaxial growth of nonpolar m-plane ZnO (10–10) on large-size LiGaO2 (100) substrates

Mitch M.C. Chou; D. R. Hang; Chenlong Chen; Yen-Hsiang Liao

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Mitch M.C. Chou

National Sun Yat-sen University

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D. R. Hang

National Sun Yat-sen University

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Chu-An Li

National Sun Yat-sen University

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Chun-Yu Lee

National Sun Yat-sen University

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Liuwen Chang

National Sun Yat-sen University

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Tao Yan

National Sun Yat-sen University

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C.N. Lu

National Sun Yat-sen University

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Jih-Jen Wu

National Cheng Kung University

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Jin-Wei Lu

National Sun Yat-sen University

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Krishna Hari Sharma

National Sun Yat-sen University

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