Nano Archive

The excitonic exchange splitting and radiative lifetime in PbSe quantum dots

An, J. M. and Franceschetti, A. and Zunger, A. (2007) The excitonic exchange splitting and radiative lifetime in PbSe quantum dots. NANO LETTERS, 7 (7). pp. 2129-2135.

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An exciton evolving from an m-fold degenerate hole level and an n-fold degenerate electron level has a nominal m x n degeneracy, which is often removed by electron-hole interactions. In PbSe quantum dots, the degeneracy of the lowest-energy exciton is m x n = 64 because both the valence-band maximum and the conduction-band minimum originate from the 4-fold degenerate (8-fold including spin) L valleys in the Brillouin zone of bulk PbSe. Using a many-particle configuration-interaction approach based on atomistic single-particle wave functions, we have computed the fine structure of the lowest-energy excitonic manifold of two nearly spherical PbSe quantum dots of radius R = 15.3 and 30.6 A. We identify two main energy splittings, both of which are accessible to experimental probe: (i) The intervalley splitting delta is the energy difference between the two near-edge peaks of the absorption spectrum. We find delta = 80 meV for R = 15.3 A and delta = 18 meV for R = 30.6 A. (ii) The exchange splitting Delta(x) is the energy difference between the lowest-energy optically dark exciton state and the first optically bright exciton state. We find that Delta(x) ranges between 17 meV for R = 15.3 A, and 2 meV for R = 30.6 A. We also find that the room-temperature radiative lifetime is tau(R) similar to 100 ns, considerably longer than the similar to 10 ns radiative lifetime of CdSe dots, in quantitative agreement with experiment.

Item Type:Article
Subjects:Material Science > Tunnelling and microscopic phenomena
Material Science > Functional and hybrid materials
ID Code:6202
Deposited By:IoN
Deposited On:09 Sep 2009 11:31
Last Modified:09 Sep 2009 11:31

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