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Resonance Fluorescence of an InGaAs Quantum Dot in a Planar Cavity Using Orthogonal Excitation and Detection

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Multiexciton absorption and multiple exciton generation in CdSe quantum dots.

Alberto Franceschetti¹, Yong Zhang

¹National Renewable Energy Laboratory, Golden, Colorado 80401, USA.

Physical Review Letters

|June 4, 2008

Summary

Multiple-exciton generation (MEG) in quantum dots is nonlinear. This study reveals that absorption bleaching is not linearly proportional to exciton number, challenging previous MEG efficiency evaluations.

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Area of Science:

Materials Science
Quantum Mechanics
Nanotechnology

Background:

Semiconductor quantum dots exhibit efficient multiple-exciton generation (MEG).
Current MEG efficiency evaluation assumes linear scaling between spectral bleaching and exciton number N(X).

Purpose of the Study:

To critically examine the assumption of linear scaling in MEG efficiency evaluation.
To investigate the relationship between spectral bleaching and exciton number in CdSe nanocrystals.

Main Methods:

Atomistic pseudopotential calculations.
Modeling carrier-carrier interactions in colloidal CdSe nanocrystals.

Main Results:

Absorption peak bleaching shows a nonlinear dependence on exciton number N(X) due to carrier-carrier interactions.
A nonlinear scaling mandates an upper bound of 1.5 for MEG-attributed normalized bleaching.
The previously assumed linear scaling predicts an upper bound of 2.0.

Conclusions:

The linear scaling assumption for MEG efficiency evaluation is inaccurate.
Normalized bleaching values exceeding 1.5 suggest contributions from mechanisms other than MEG.
Accurate MEG characterization requires accounting for nonlinear carrier interactions.