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

QD samples – as grown and annealed CdTe = 4 ML ZnTe ~50 nm GaAs ZnTe ~1  m CdTe ~4  m Z

Effects of annealing E g (CdTe) E g (ZnTe) ZnTe CdTe E g ( Cd 1-x Zn x Te ) E g (Zn 1-x Cd x Te) Zn 1-x Cd x Te Cd 1-x Zn x Te As-grown QDs Annealed QDs inter-diffusion of Zn and Cd  increases average dot size  Shallower confining potential  Shifts energy to higher value Zn 1-x Cd x Te

Resonant Raman Intensity 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? h  excitation hW LO h  scattered

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 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

Effects of annealing E g (CdTe) E g (ZnTe) ZnTe CdTe E g ( Cd 1-x Zn x Te ) E g (Zn 1-x Cd x Te) Zn 1-x Cd x Te Cd 1-x Zn x Te As-grown QDs Annealed QDs inter-diffusion of Zn and Cd  increases average dot size  Shallower confining potential  Shifts energy to higher value Zn 1-x Cd x Te

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-grown QDs.

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)