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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).
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 hexcitation hscattered 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
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)