Journal
ACS NANO
Volume 6, Issue 9, Pages 8325-8334Publisher
AMER CHEMICAL SOC
DOI: 10.1021/nn303060r
Keywords
type-II nanostructures; isoelectronically doped nanocrystals; electronic and optical property; exciton
Categories
Funding
- US Department of Energy, Office of Science, Basic Energy Sciences [DE-AC36-08GO28308]
- Renewable Energy Materials Research Science and Engineering Center (NSF) at the Colorado School of Mines [DMR-0820518]
- National Renewable Energy Laboratory
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [0820518] Funding Source: National Science Foundation
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CdTe/CdSe core/shell nanocrystals are the prototypical example of type-II nanoheterostructures, in which the electron and the hole wave functions are localized in different parts of the nanostructure. As the thickness of the CdSe shell increases above a few monolayers, the spectroscopic properties of such nanocrystals change dramatically, reflecting the underlying type-I -> type-II transition. For example, the exciton Stokes shift and radiative lifetime increase, while the decreasing biexciton binding energy changes sign from positive to negative. Recent experimental results for CdSe nanocrystals isoelectronically doped with a few Te substitutional impurities, however, have revealed a very different dependence of the optical and electronic properties on the nanocrystal size. Here we use atomistic calculations based on the pseudopotential method for single-particle excitations and the configuration-interaction approach for many-particle excitations to investigate cattier localization and electronic properties of CdTe/CdSe nanocrystals as the size of the (die core decreases from a few nm (characteristic of core/shell CdTe/CdSe nanocrystals) to the single impurity limit. We find that the unusual spectroscopic properties of isoelectronically doped CdSe:Te nanocrystals can be rationalized in terms of the change in the localization volume of the electron and hole wave functions as the size of the nanocrystal increases. The size dependence of the exciton Stokes shift, exciton radiative lifetime, and biexciton binding energy reflects the extent of carrier localization around the Te impurities.
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