教師著作
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Item Nanohomojunction (GaN) and nanoheterojunction (InN) nanorods on one-dimensional GaN nanowire substrates(Wiley-VCH Verlag, 2004-03-01) Z.-H. Lan; C.-H. Liang; C.-W. Hsu; C.-T. Wu; H.-M. Lin; S. Dhara; K.-H. Chen; L.-C. Chen; Chia-Chun ChenThe formation of homojunctions and heterojunctions on two-dimensional (2D) substrates plays a key role in the device performance of thin films. Accelerating the progress of device fabrication in nanowires (NWs) also necessitates a similar understanding in the one-dimensional (1D) system. Nanohomojunction (GaN on GaN) and nanoheterojunction (InN on GaN) nanorods (NRs) were formed in a two-step growth process by a vapor–liquid–solid (VLS) mechanism. Ga2O3 nanoribbons were formed using Ni as catalyst in a chemical vapor deposition (CVD) technique and then completely converted to GaN NWs with NH3 as reactant gas. An Au catalyst is used in the second step of the VLS process to grow GaN and InN NRs on GaN NWs using CVD techniques. A morphological study showed the formation of nanobrushes with different structural symmetries and sub-symmetries in both homogeneous and heterogeneous systems. Structural characterizations showed nearly defect-free growth of nanohomojunction (GaN) and nanoheterojunction (InN) NRs on 1D GaN NW substrates.Item Blueshift of yellow luminescence band in self-ion-implanted n-GaN nanowire(American Institute of Physics (AIP), 2004-05-03) S. Dhara; A Datta; C.-T. Wu; Z.-H. Lan; K.-H. Chen; Y. -L. Wang; Y.-F. Chen; C.-W. Hsu; L.-C. Chen; H.-M. Lin; Chia-Chun ChenOptical photoluminescence studies are performed in self-ion (Ga+)-implanted nominally dopedn-GaNnanowires. A 50 keV Ga+focused ion beam in the fluence range of 1×1014–2×1016 ions cm−2 is used for the irradiation process. A blueshift is observed for the yellow luminescence (YL) band with increasing fluence. Donor–acceptor pair model with emission involving shallow donor introduced by point-defect clusters related to nitrogen vacancies and probable deep acceptor created by gallium interstitial clusters is responsible for the shift. High-temperature annealing in nitrogen ambient restores the peak position of YL band by removing nitrogen vacancies.Item Interband Optical Transitions in GaN Nanotubes Encapsulated GaP nanowires(AMERICAN PHYSICAL SOCIETY, 2003-04-30) M.-W. Lee; H.-C. Hseuh; H.-M. Lin; Chia-Chun ChenThis work investigates the optical properties of cylindrical GaP nanowires encapsulated inside GaN nanotubes (GaP@GaN). Many absorption structures are observed in the range of 2.0–4 eV. Calculations are performed to determine the quantized energy levels of electrons and holes confined in the GaP well. Analytical results indicate that the absorption peaks are attributable to interband optical transitions due to the confined carriers in the heterostructure.Item Synthesis and Characterization of Core-Shell GaP@GaN and GaN@GaP Nanowires(American Chemical Society, 2003-04-09) H.-M. Lin; Y.-L. Chen; J. Yang; Y.-C. Liu; K.-M. Yin; J.-J. Kai; F.-R. Chen; L.-C. Chen; Y.-F. Chen; Chia-Chun ChenA convenient thermal CVD route to core−shell GaP@GaN and GaN@GaP nanowires is developed. The structural analyses indicate that the nanowires exhibit a two-layer and wirelike structure. High-resolution transmission electron microscopy (HRTEM) images reveal misfit dislocation loops at the interface of the nanowires. Unusual temperature dependences of the photoluminescence (PL) intensity of GaP@GaN nanowires are observed, and they are interpreted by the piezoelectric effect induced from lattice mismatch between two semiconductor layers. In the Raman spectra of GaN@GaP nanowires, an unexpected peak at 386 cm-1 is found and assigned to a surface phonon mode.Item Electronic Structure of GaN Nanowire Studied by x-ray-Absorption Spectroscopy and Scanning Photoelectron Microscopy(American Institute of Physics(AIP) Publishing, 2003-06-02) J.-W. Chiou; J.-C. Jan; H.-M. Tsai; W.-F. Pong; M.-H. Tsai; I.-H. Hong; R. Rklauser; J.-F. Lee; C.-W. Hsu; H.-M. Lin; Chia-Chun Chen; C.-H. Shen; L.-C. Chen; K.-H. ChenX-ray absorption near edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been employed to obtain information on the electronic structures of the GaN nanowires and thin film. The comparison of the XANES spectra revealed that the nanowires have a smaller (larger) N (Ga) K edge XANES intensity than that of the thin film, which suggests an increase (decrease) of the occupation of N 2p (Ga 4p) orbitals and an increase of the N (Ga) negative (positive) effective charge in the nanowires. The SPEM spectra showed that the Ga 3d band for the nanowires lies about 20.8 eV below the Fermi level and has a chemical shift of about -0.9 eV relative to that of the thin film. © 2003 American Institute of Physics.Item Characterization of Nanodome on GaN Nanowires Formed with Ga Ion Irradiation(Nihon Kinzoku Gakkai, 2004-01-01) S. Muto; S. Dahara; A. Datta; C.-W. Hsu; C.-T. Wu; C.-H. Shen; L. -C. Chen; K.-H. Chen; Y.-L. Wang; T. Tanabe; T. Maruyama; H.-M. Lin; Chia-Chun ChenStructure of nano-domes formed by Ga+ ion irradiation with a focused ion beam (FIB) apparatus onto GaN nanowires (NWs) was examined with conventional transmission electron microscopy (CTEM), electron energy-loss spectroscopy (EELS) and energy-filtering TEM (EF-TEM). The nano-dome consisted of metallic gallium, covered by a GaN layer, the structure of which is amorphous or liquid. It is considered that the dome structure is formed by preferential displacement of lighter element (N) and agglomeration of heavier one (Ga). 1 MeV electron irradiation onto the sample pre-irradiated by Ga+ ions at a dose below the threshold for the dome formation induced the N2 bubble formation without segregating Ga atoms, which suggests the radiation-enhanced diffusion (RED) of heavy atoms plays an important role in the nano-dome formation.Item Enhanced Dynamic Annealing in Ga+ ion-implanted GaN Nanowires(American Institute of Physics(AIP) Publishing, 2003-01-20) S. Dhara; A. Datta; C.-T. Wu; Z.-H. Lan; K.-H. Chen; Y.-L. Wang; L.-C. Chen; C.-W. Hsu; H.-M. Lin; Chia-Chun ChenGa+ion implantation of chemical-vapor-deposited GaNnanowires (NWs) is studied using a 50-keV Ga+focused ion beam. The role of dynamic annealing (defect-annihilation) is discussed with an emphasis on the fluence-dependent defect structure. Unlike heavy-ion-irradiated epitaxialGaN film, large-scale amorphization is suppressed until a very high fluence of 2×1016 ions cm−2. In contrast to extended-defects as reported for heavy-ion-irradiated epitaxialGaN film, point-defect clusters are identified as major component in irradiated NWs. Enhanced dynamic annealing induced by high diffusivity of mobile point-defects in the confined geometry of NWs is identified as the probable reason for observed differences.