Multiexcitons in type-II colloidal semiconductor quantum dots

Dan Oron, Miri Kazes, Uri Banin

Research output: Contribution to journalArticle

167 Citations (Scopus)

Abstract

The spectroscopy and dynamics of multiple excitations on colloidal type-II CdTe/CdSe core-shell quantum dots (QDs) are explored via quasi-cw multiexciton spectroscopy. The charge separation induced by the band offset redshifts the exciton emission and increases the radiative lifetime. In addition, we observe a significant modification of multiexciton properties compared with core-only or type-I QDs. In particular, the Auger recombination lifetimes are significantly increased, up to a nanosecond time scale. While in type-I QDs the Auger lifetime scales with the volume, we find for type-II QDs a scaling law that introduces a linear dependence also on the radiative lifetime. We observe a blueshift of the biexciton emission and extract biexciton repulsion of up to 30 meV in type-II QDs. This is assigned to the dominance of the Coulomb repulsion as the positive and negative charges become spatially separated, which overwhelms the correlation binding term. Higher electronic excited states can remain type I even when the lowest transition is already type II, resulting in a different size dependence of the triexciton emission. Finally, we discuss the possibilities of "multiexciton band gap engineering" using colloidal type-II QDs.

Original languageEnglish
Article number035330
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume75
Issue number3
DOIs
Publication statusPublished - 2007

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Semiconductor quantum dots
quantum dots
radiative lifetime
Spectroscopy
life (durability)
Scaling laws
polarization (charge separation)
Excited states
Excitons
scaling laws
spectroscopy
excitation
Energy gap
excitons
engineering
electronics

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Multiexcitons in type-II colloidal semiconductor quantum dots. / Oron, Dan; Kazes, Miri; Banin, Uri.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 75, No. 3, 035330, 2007.

Research output: Contribution to journalArticle

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AB - The spectroscopy and dynamics of multiple excitations on colloidal type-II CdTe/CdSe core-shell quantum dots (QDs) are explored via quasi-cw multiexciton spectroscopy. The charge separation induced by the band offset redshifts the exciton emission and increases the radiative lifetime. In addition, we observe a significant modification of multiexciton properties compared with core-only or type-I QDs. In particular, the Auger recombination lifetimes are significantly increased, up to a nanosecond time scale. While in type-I QDs the Auger lifetime scales with the volume, we find for type-II QDs a scaling law that introduces a linear dependence also on the radiative lifetime. We observe a blueshift of the biexciton emission and extract biexciton repulsion of up to 30 meV in type-II QDs. This is assigned to the dominance of the Coulomb repulsion as the positive and negative charges become spatially separated, which overwhelms the correlation binding term. Higher electronic excited states can remain type I even when the lowest transition is already type II, resulting in a different size dependence of the triexciton emission. Finally, we discuss the possibilities of "multiexciton band gap engineering" using colloidal type-II QDs.

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