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Probing Excited States in Self-a ssembled Quantum Dots with Resonant Raman Scattering. A. Abdi , T. B. Hoang, S. Mackowski, L. M. Smith and H. E. Jackson Department of Physics, University of Cincinnati, Ohio 45221-0011 J. M. Yarrison-Rice

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Probing Excited States in

Self-assembled Quantum Dots with

Resonant Raman Scattering

A. Abdi, T. B. Hoang, S. Mackowski, L. M. Smith and H. E. Jackson

Department of Physics, University of Cincinnati, Ohio 45221-0011

J. M. Yarrison-Rice

Department of Physics, Miami University, Oxford, OH

J. Kossut and G. Karczewski

Institute of Physics Polish Academy of Sciences, Warsaw, Poland

Supported by NSF(United States) and CELDIS (Poland).


Qd samples as grown and annealed

ZnTe ~50 nm

ZnTe ~1 mm

CdTe ~4 mm

GaAs

QD samples – as grown and annealed

CdTe = 4 ML

Z


Effects of annealing

As-grown QDs

Annealed QDs

ZnTe

ZnTe

CdTe

Eg (ZnTe)

Eg(CdTe)

Effects of annealing

  • inter-diffusion of Zn and Cd

    • increases average dot size

    • Shallower confining potential

    • Shifts energy to higher value

Zn1-xCd xTe

Zn1-xCd xTe

Cd1-xZnxTe

Eg (Zn1-xCd xTe)

Eg(Cd1-xZnxTe)


Resonant raman intensity

hWLO

hexcitation

hscattered

Resonant Raman Intensity

  • Our group has studied excited states of CdTe QDs by resonant PL and a single QD PLE techniques at 6K.

  • T. A. Nguyen, S. Mackowski, H. E. Jackson and L.M. Smith Phys. Rev. B 70 (2004)

  • Can we study the excited state of QDs by Resonant Raman Scattering at room temperature?


Typical resonant raman spectrum at room temperature
Typical Resonant Raman spectrum at room temperature

  • 1LO and 2LO ZnTe phonon appear at 202 cm-1 and 404 cm-1

  • We analyze 1LO resonance to probe excited state in CdTe QDs


Znte 1lo raman intensity vs excitation energy for as grown sample
ZnTe 1LO Raman intensity vs. excitation energy for as-grown sample



Photoluminescence temperature dependence
Photoluminescence temperature sampledependence

  • Room temperature ground state at 1.962 eV





Effects of annealing1

As-grown QDs energy: annealed CdTe QDs

Annealed QDs

ZnTe

ZnTe

CdTe

Eg (ZnTe)

Eg(CdTe)

Effects of annealing

  • inter-diffusion of Zn and Cd

    • increases average dot size

    • Shallower confining potential

    • Shifts energy to higher value

Zn1-xCd xTe

Zn1-xCd xTe

Cd1-xZnxTe

Eg (Zn1-xCd xTe)

Eg(Cd1-xZnxTe)


Summary
Summary energy: annealed CdTe QDs

  • We have utilized Resonant Raman scattering to observe the excited state energy distribution from as-grown and annealed CdTe QDs.

  • The ground state - excited state energy difference is larger for as-grown sample, as expected.

  • The excited state energy distribution for annealed QDs is narrower vs. as-grownQDs.


Evidence for excited state
Evidence for excited state energy: annealed CdTe QDs

  • Excited state is 100 mev above ground state

  • Profile of excited state is similar with that of ground state

T. A. Nguyen, S. Mackowski, H. E. Jackson and L.M. Smith Phys. Rev. B 70 (2004)


Photoluminescence excitation spectrum
Photoluminescence excitation Spectrum energy: annealed CdTe QDs

T. A. Nguyen, S. Mackowski, H. E. Jackson and L.M. Smith Phys. Rev. B 70 (2004)


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