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    Please use this identifier to cite or link to this item: http://nccur.lib.nccu.edu.tw/handle/140.119/63540

    Title: Excitonic effects in the optical properties of a SiC sheet and nanotubes
    Authors: 郭光宇
    Hsueh,H. C.;Guo, Guang-Yu;Louie, Steven G.
    Contributors: 應物所
    Date: 2011.08
    Issue Date: 2014-01-24 12:37:44 (UTC+8)
    Abstract: The quasiparticle band structure and optical properties of single-walled zigzag and armchair SiC nanotubes (SiC-NTs) as well as a single SiC sheet are investigated by ab initio many-body calculations using the GW and the GW plus Bethe-Salpeter equation approaches, respectively. Significant GW quasiparticle corrections, of more than 1.0 eV, to the Kohn-Sham band gaps from the local density approximation (LDA) calculations are found. The GW self-energy corrections transform the SiC sheet from an indirect LDA band gap to a direct band gap material. Furthermore, the quasiparticle band gaps of SiC-NTs with different chiralities behave very differently as a function of tube diameter, and this can be attributed to the difference in the curvature-induced orbital rehybridization among the different chiral nanotubes. The calculated optical absorption spectra are dominated by discrete exciton peaks due to exciton states with a high binding energy, up to 2.0 eV, in the SiC sheet and SiC-NTs. The formation of strongly bound excitons is attributed to the enhanced electron-hole interaction in these low-dimensional systems. Remarkably, the excited electron amplitude of the exciton wave function is found to peak on Si atoms near the hole position (which is on the C site) in zigzag SiC-NTs, indicating a charge transfer from an anion (hole) to its neighboring cations by photoexcitation. In contrast, this pronounced peak structure disappears in the exciton wave function in armchair SiC-NTs. Furthermore, in armchair SiC-NTs, the bound exciton wave functions are more localized and also strongly cylindrically asymmetric. The high excitation energy, 3.0 eV, of the first bright exciton, with no dark exciton below it, suggests that small-radius armchair SiC-NTs could be useful for optical devices working in the UV regime. On the other hand, zigzag SiC-NTs have many dark excitons below the first bright exciton and hence may have potential applications in tunable optoelectric devices ranging from infrared to UV frequencies by external perturbations.
    Relation: Physical Review B, 84(8), 085404
    Source URI: http://link.aps.org/doi/10.1103/PhysRevB.84.085404
    Data Type: article
    DOI 連結: http://dx.doi.org/10.1103/PhysRevB.84.085404
    DOI: 10.1103/PhysRevB.84.085404
    Appears in Collections:[應用物理研究所 ] 期刊論文

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