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Author: search.filters.author.Chen, WHHas files: No

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    Growth and X-ray characterization of an InN film on sapphire prepared by metalorganic vapor phase epitaxy
    (1997-12-15)
    Chen, WK
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    Pan, YC
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    Lin, HC
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    Ou, J
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    Chen, WH
    We report the successful growth of an InN film by metalorganic vapor phase epitaxy. The film quality is found to be strongly dependent on the growth temperature and the TMIn reactant flow rate. The best quality epilayer was obtained at 375 degrees C under a high V/III ratio growth environment. It exhibits a FWHM of the X-ray rocking curve as narrow as 96 arcsec: which explains the superior crystalline quality of our epitaxial film.
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    Photoluminescence studies of GaN films of different buffer layer and doping concentration
    (1998-02-01)
    Shen, CC
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    Shu, CK
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    Lin, HC
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    Ou, J
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    Chen, WK
    Photoluminescence (PL) measurements of GaN films with various buffer thicknesses and Si-doping concentrations have been carried out. PL response of one specific sample was studied for temperature dependence. The results showed that the band gap energy reduction is linearly proportional to the temperature increase with a slope of similar to-4 x 10(-4) eV.K-1 and that the activation energies for donor-bound and acceptor-bound exciton transitions are 15 and 18 meV, respectively. In Si-doped GaN films, the PL data indicated that the reduced gap depends on the third power of carrier concentration as n(1/3). We also obtained a concentration coefficient of 2.34 x 10(-4) eV.cm and a band gap energy of 3.426 eV in the undoped GaN film.
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    Phonon-plasmon interaction in GaN films studied by Raman scattering
    (1998-02-01)
    Shen, CC
    ;
    Shu, CK
    ;
    Lin, HC
    ;
    Chen, WK
    ;
    Chen, WH
    GaN films of different buffer thicknesses (from 0 to 600 Angstrom) were grown on (0001) sapphire using MOCVD. The epitaxial films show autodoping with carrier concentration ranging from 8 x 10(16) to 5 x 10(17) cm(-3) as determined by Hall measurements. The Raman scattering reveals that the A(1)(LO) mode shifts from 733 to 740 cm(-1) as a result of the phonon-plasmon interaction.
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    Raman and x-ray studies of InN films grown by metalorganic vapor phase epitaxy
    (1998-11-02)
    Lee, MC
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    Lin, HC
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    Pan, YC
    ;
    Shu, CK
    ;
    Ou, J
    Thin InN films were deposited on the (0001) sapphire substrate at various temperatures from 325 to 600 degrees C by metalorganic vapor phase epitaxy. We used Raman scattering and x-ray diffraction to investigate the film properties and crystalline structures. Significant line broadening, softening and intensity evolution were observed at the growth temperatures between 375 and 450 degrees C. This can be attributed to the formation of the mixed hexagonal and cubic structures and the related dislocation defects. As the growth temperature is further increased, the hexagonal phase is found to be dominant in the deposited InN film. (C) 1998 American Institute of Physics. [S0003-6951(98)00744-X].
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    The electronic structure and optical properties of phosphorus implanted GaN films
    (2000)
    Shu, CK
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    Lee, WH
    ;
    Huang, HY
    ;
    Chuang, CH
    ;
    Chen, WK
    We have studied optical and electronicc transition properties of GaN layers grown by MOCVD which are implanted by isoelectronic impurities of phosphorus (P). The P-implanted samples were treated by rapid thermal annealing to recover implantation-induced damages. A strong emission band around 430 nm were observed in P-implanted sample due to the recombination of bound exciton to P-hole isoelectronic traps. From the Arrhenius plot, the hole binding energy about 180 meV localized at the P-isoelectronic trap and the exciton localization energy of 28 meV were obtained. According to first-principle total-energy calculations, we suggest that the implantation likely induces N-I or P-related defects. From the PLE, we found that the absorption by band-to-band and shallow donors dominates the yellow luminescence (YL) and the implantation of P has induced localized states that not only increase the YL but also suppress the transition from the free electron-hole pairs to the deep-levels.
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    Long-term photocapacitance decay behavior in undoped GaN
    (2000)
    Chung, HM
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    Pan, YC
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    Chung, WC
    ;
    Chen, NC
    ;
    Tsai, CC
    We have employed the photocapacitance measurement to examine the physical properties of GaN Schottky diode made from the undoped epilayer grown by metalorganic vapor phase epitaxy. The resulted transient capacitance spectrum shows that the diode exhibits a characteristic of long-term logarithmic-type decaying behavior, which, we believe, is correlated closely to the linear arranged traps close to the core of the threading edge dislocations.
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    Effects in carrier dynamics of Isolectronic In doped in GaN films grown by metalorganic vapor phase epitaxy
    (2000)
    Huang, HY
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    Shu, CK
    ;
    Lin, WC
    ;
    Liao, KC
    ;
    Chuang, CH
    Time-resolved photoluminescence spectra were used to characterize isoelectronically doped GaN:In films. Our results indicate that the recombination lifetime of donor-bound-exciton transition of pure GaN exhibits strong dependence on temperature. When In is doped into GaN, the recombination lifetime decreases sharply from 68 ps to 30 ps, irregardless of measured temperature and In doping concentration. The cause for this appearance is not clear at present. It might be related to the isoelectronic In impurity itself in GaN, which creates shallow energy levels that predominate the recombination process.
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    Symmetric 3D passive components for RF ICs application
    (2003)
    Chen, WZ
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    Chen, WH
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    電子工程學系及電子研究所
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    Department of Electronics Engineering and Institute of Electronics
    This paper proposes novel 3-D symmetric RF passive components, including inductors, transformers, and baluns. Layout areas of these components are drastically reduced by means of stacked structure while the symmetry of input and output ports is also maintained. The area saving of 3-D inductor is up 70 %. The 1:1 transformer shows less than 0.1 % inductance mismatch in a 18 GHz range, and K is up to 0.87 at 17 GHz. The 3-D balun manifests less than 0.8 dB gain mismatch from 5.25GHz to 6GHz and phase error is about 4degrees at 5.25 GHz according to measurement results. All the components are fabricated in a 0.18 mum standard CMOS process.
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    Symmetric 3D passive components for RE ICs application
    (2003)
    Chen, WZ
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    Chen, WH
    ;
    電子工程學系及電子研究所
    ;
    Department of Electronics Engineering and Institute of Electronics
    This paper proposes novel 3-D symmetric RF passive components, including inductors, transformers, and baluns. Layout areas of these components are drastically reduced by means of stacked structure while the symmetry of input and output ports is also maintained. The area saving of 3-D inductor is up 70 %. The 1:1 transformer shows less than 0.1 % inductance mismatch in a 18 GHz range, and K is up to 0.87 at 17 GHz. The 3-D balun manifests less than 0.8 dB gain mismatch from 5.25GHz to 6GHz and phase error is about 4degrees at 5.25 GHz according to measurement results. All the components are fabricated in a 0.18 mum standard CMOS process.
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    Task-stage knowledge support: Coupling user information needs with stage identification
    (2005)
    Wu, IC
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    Liu, DR
    ;
    Chen, WH
    ;
    資訊管理與財務金融系 註：原資管所+財金所
    ;
    Department of Information Management and Finance
    Effective knowledge support in knowledge-intensive environments can place great demands on information filtering (IF) strategies. An IF system that relies on traditional information retrieval technology and user models (e.g., user profiles) is regarded as an effective approach for supporting long-term information needs. To provide a more effective knowledge support, we propose a task-stage knowledge support model that incorporates the advantages of the traditional IF model with the characteristics of each task-stage. A correlation analysis method is proposed to determine a worker's task-stage (e.g., pre-focus, focus formulation, and post-focus task stages), and an ontology-based topic discovery method is proposed to examine the variety of a worker's information needs for specific topics. Consequently, the knowledge support is achieved by coupling user information needs with task-stage identification.