Yazar "Demir, Hilmi Volkan" seçeneğine göre listele

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    Reordering orbitals of semiconductor multi-shell quantum dot-quantum well heteronanocrystals
    (AMER INST PHYSICS, 2012) Sahin, Mehmet; Nizamoglu, Sedat; Yerli, Ozan; Demir, Hilmi Volkan
    Based on self-consistent computational modeling of quantum dot-quantum well (QDQW) heteronanocrystals, we propose and demonstrate that conduction-electron and valence-hole orbitals can be reordered by controlling shell thicknesses, unlike widely known core/shell quantum dots (QDs). Multi-shell nanocrystals of CdSe/ZnS/CdSe, which exhibit an electronic structure of 1s-1p-2s-2p-1d-1f for electrons and 1s-1p-2s-2p-1d-2d for holes using thin ZnS and CdSe shells (each with two monolayers), lead to 1s-2s-1p-1d-1f-2p electron-orbitals and 1s-2s-1p-1d-2p-1f hole orbitals upon increasing the shell thicknesses while keeping the same core. This is characteristically different from the only CdSe core and CdSe/ZnS core/shell QDs, both exhibiting only 1s-1p-1d-2s-1f-2p ordering for electrons and holes. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3678585]
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    Öğe
    Self-consistent computation of electronic and optical properties of a single exciton in a spherical quantum dot via matrix diagonalization method
    (AMER INST PHYSICS, 2009) Sahin, Mehmet; Nizamoglu, Sedat; Kavruk, A. Emre; Demir, Hilmi Volkan
    In this study, we develop and demonstrate an efficient self-consistent calculation schema that computes the electronic structure and optical properties of a single exciton in a spherical quantum dot (QD) with an interacting pair of electron and hole wave functions. To observe modifications on bands, wave functions, and energies due to the attractive Coulomb potential, the full numeric matrix diagonalization technique is employed to determine sublevel energy eigenvalues and their wave functions in effective mass approximation. This treatment allows to observe that the conduction and valance band edges bend, that the electron and hole wave functions strongly localize in the QD, and that the excitonic energy level exhibits redshift. In our approach for the Coulomb term between electron and hole, the Poisson-Schrodinger equations are solved self-consistently in the Hartree approximation. Subsequently, exciton binding energies and associated optical properties are computed. The results are presented as a function of QD radii and photon energies. We conclude that all of these numerical results are in agreement with the experimental studies. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3197034]