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


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

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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).


ZnTe ~50 nm

ZnTe ~1 mm

CdTe ~4 mm

GaAs

QD samples – as grown and annealed

CdTe = 4 ML

Z


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)


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

  • 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 annealed sample


Photoluminescence temperature dependence

  • Room temperature ground state at 1.962 eV


Raman and non-resonance PL intensities vs. excitation energy:as-grown CdTe QDs


Raman and non-resonance PL intensities vs. excitation energy: annealed CdTe QDs


Comparison of as grown and annealed excited states


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)


Summary

  • 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

  • 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

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


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