Multiexciton spectroscopy of semiconductor nanocrystals under quasi-continuous-wave optical pumping

Dan Oron, Miri Kazes, Itzik Shweky, and Uri Banin
Phys. Rev. B 74, 115333 – Published 27 September 2006

Abstract

We present a method for performing multiexciton spectroscopy in colloidal semiconductor nanocrystals. In this regime multiexcitonic states are generated sequentially via a “ladder-climbing” mechanism. The distribution of multiexcitonic states, determined by a steady-state rate equation, adiabatically follows the illumination intensity, allowing for “slow” detection of multiexcitonic spectra. Emission spectra of multiexcitonic states with a small number of excitons are obtained without passing through states with a large number of excitons. This is in contrast with impulsive excitation schemes utilizing picosecond pulses, where in order to significantly populate a given multiexcitonic state, many of the dots necessarily pass through states with a larger number of excitons due to the Poissonian distribution of the number of absorbed photons. In particular, we observe directly the order of appearance of the various multiexcitonic peaks. This enables us to determine the threshold conditions for Auger ionization, shedding more light on the nature of this process. We are also able to observe the short-lived excitations at higher energies than triexcitons in CdSe quantum dots. Finally, we demonstrate bi- and triexcitonic optical gain in a close-packed film under quasi-continuous-wave pumping.

    • Received 23 July 2006

    DOI:https://doi.org/10.1103/PhysRevB.74.115333

    ©2006 American Physical Society

    Authors & Affiliations

    Dan Oron, Miri Kazes, Itzik Shweky, and Uri Banin

    • The Institute of Chemistry and the Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem 91904, Israel*

    • *URL: http://chem.ch.huji.ac.il/∼nano/

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    Issue

    Vol. 74, Iss. 11 — 15 September 2006

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