Fine structure and size dependence of exciton and bi-exciton optical spectra in CdSe nanocrystals

Abstract

Theory of electronic and optical properties of exciton and bi-exciton complexes confined in CdSe spherical nanocrystals is presented. The electron and hole states are computed using atomistic $s{p}^3{d}^5{s}^{\ast }$ tight binding Hamiltonian including an effective crystal field splitting, spin-orbit interactions, and model surface passivation. The optically excited states are expanded in electron-hole configurations and the many-body spectrum is computed in the configuration-interaction approach. Results demonstrate that the low-energy electron spectrum is organized in shells ($s$, $p$, ...), whilst the valence hole spectrum is composed of four low-lying, doubly degenerate states separated from the rest by a gap. As a result, the bi-exciton and exciton spectrum is composed of a manifold of closely lying states, resulting in a fine structure of exciton and bi-exciton spectra. The quasi-degenerate nature of the hole spectrum results in a correlated bi-exciton state, which makes it slowly convergent with basis size. We carry out a systematic study of the exciton and bi-exciton emission spectra as a function of the nanocrystal diameter and find that the interplay of repulsion between constituent excitons and correlation effects results in a change of the sign of bi-exciton binding energy from negative to positive at a critical nanocrystal size.

13 pages

References in corpus (4)

• Carrier multiplication yields in PbS and PbSe nanocrystals measured by transient photoluminescence
• Carrier multiplication yields in CdSe and CdTe nanocrystals by transient photoluminescence
• Distribution of carrier multiplication rates in CdSe and InAs nanocrystals
• Anomalous circular polarization of magneto-photoluminescence from individual CdSe nanocrystals

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• Tuning biexciton binding and anti-binding in core/shell quantum dots
• Coulomb matrix elements for the impact ionization process in nanocrystals: the envelope function approach
• Trions and biexcitons in a nanowire
• Accurate and efficient description of interacting carriers in quantum nanostructures by selected configuration interaction and perturbation theory
• Inter-band Coulomb coupling in narrow gap semiconductor nanocrystals: $\mathbf{k}\cdot \mathbf{p}$ theory
• Dynamics of dissipative multiple exciton generation in nanocrystals
• Efficiency of the coherent biexciton admixture mechanism for multiple exciton generation in InAs nanocrystals