The near band-gap level structure in high-quality colloidal InAs nanocrystal quantum dots within the very strong confinement regime is investigated. Size-selective photoluminescence excitation and fluorescence line narrowing measurements reveal a size-dependent splitting between the absorbing and the emitting states. The splitting is assigned to the confinement-enhanced electron - hole exchange interaction. The size dependence of the splitting significantly deviates from the idealized 1/r3 scaling law for the exchange splitting. A model incorporating a finite barrier which allows for wavefunction leakage is introduced. The model reproduces the observed 1/r2 dependence of the splitting and good agreement with the experimental data is obtained. The smaller barriers for embedded InAs dots grown by molecular-beam epitaxy, are predicted to result in smaller exchange splitting as compared with colloidal dots with a similar number of atoms.
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Acknowledgements—U.B. thanks the Rothschild and Fulbright foundations for support. We thank Dr W. Jaskolski for assistance in the overlap calculations and Dr Al. L. Efros for helpful discussions. This work was supported by the U.S. National Science Foundation under contract number DMR-9505302.
- Exchange splitting
- Quantum dots
- Semiconductor nanocrystal