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

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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  1. 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).

  2. ZnTe ~50 nm ZnTe ~1 mm CdTe ~4 mm GaAs QD samples – as grown and annealed CdTe = 4 ML Z

  3. 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)

  4. 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?

  5. 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

  6. ZnTe 1LO Raman intensity vs. excitation energy for as-grown sample

  7. ZnTe 1LO Raman intensity vs. excitation energy for annealed sample

  8. Photoluminescence temperature dependence • Room temperature ground state at 1.962 eV

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

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

  11. Comparison of as grown and annealed excited states

  12. 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)

  13. 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.

  14. 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)

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

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