Excitonic Exchange Splitting and Radiative Lifetime in PbSe Quantum Dots
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 {angstrom}. We identify two main energy splittings, both of which are accessible to experimental probe: (i) The intervalley splitting is the energy difference between the two near-edge peaks of the absorption spectrum. We find {delta} = 80 meV for R = 15.3 {angstrom} and {delta} = 18 meV for R = 30.6 {angstrom}. (ii) The exchange splitting {Delta}{sub x} is the energy difference between the lowest-energy optically dark exciton state and the first optically bright exciton state. We find that {Delta}{sub x} ranges between 17 meV for R = 15.3 {angstrom}, and 2 meV for R = 30.6 {angstrom}. We also find that the room-temperature radiative lifetime is {tau}{sub R} {approx} 100 ns, considerably longer than the {approx}10 ns radiative lifetime of CdSe dots, in quantitative agreement with experiment.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC36-99-GO10337
- OSTI ID:
- 939525
- Journal Information:
- Nano Letters, Vol. 7, Issue 7, 2007
- Country of Publication:
- United States
- Language:
- English
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