M. Khoshnegar, A. H. Majedi
The electronic and spectroscopic properties of quantum dots (QD) embedded inside [001]- and [111]-oriented zinc-blende nanowires are investigated. Phase coherence of exciton-photon wavefunction is enhanced owing to the elevated symmetry characters (C3v or D2d) exhibited by the single particle orbitals localized in this type of QDs, offering them as ideal sources of polarization-entangled photons. We focus on cylindrical, cone-shaped and hexagonal QDs and discuss band mixing effects and spin coherence time by the inclusion of strain-induced confinements and spin-orbit interaction. We demonstrate how the QD radius, vertical aspect ratio and elongation may influence the electronic properties by manipulating the single particle dispersion relations along with their orbital extents. The energy ordering of ground-state exciton X0, biexciton XX0 and trions relies on direct, correlation and exchange Coulomb interactions between their constituting particles. We numerically calculate these energy terms by employing the configuration interaction method and elaborate the results qualitatively. Difference between the direct interaction terms, and thus the binding energies of few-particle complexes, is suppressed when the vertical and lateral confinements become comparable. Then exerting lateral or vertical electric fields may renormalize the binding energies realizing a transition from binding to anti-binding regime or reverse. Resolving this transition is essential for generating entangled photons in the time reordering scheme. Results addressed here show how dimensions and growth orientations affect the performance of these QDs as entangled photon sources.
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http://arxiv.org/abs/1204.4775
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