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Absorption and generation of light with silicon nanocrystals in SiO 2

Absorption and generation of light with silicon nanocrystals in SiO 2. Dolf Timmerman Van der Waals-Zeeman Institute University of Amsterdam. Amsterdam Master of Physics Symposium 2008. Silicon. Photonics. Silicon is a poor light-emitter. Dolf Timmerman.

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Absorption and generation of light with silicon nanocrystals in SiO 2

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  1. Absorption and generation of light with silicon nanocrystals in SiO2 Dolf Timmerman Van der Waals-Zeeman Institute University of Amsterdam Amsterdam Master of Physics Symposium 2008

  2. Silicon Photonics • Silicon is a poor light-emitter Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam • Indirect bandgap • Transitions need to overcome Δk • Radiative transitions phonon assisted Amsterdam Master of Physics Symposium 2008

  3. Nanocrystals Si NC • Bandgap modification induced by quantum confinement • Bands  quantized energy levels • Relaxation of k-vector conservation rule, in relation to indirect bandgap (Heisenberg) • Tuning optical properties Dolf Timmerman 4.3 nm Silicon Van der Waals-Zeeman Institute | University of Amsterdam Amsterdam Master of Physics Symposium 2008

  4. Sample Optical active layer containing silicon nanocrystals (and erbium) Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam 2 μm SiO2 Si - NC Sample preparation, Kobe University 3.1 nm σ = 14% Amsterdam Master of Physics Symposium 2008

  5. Setup λ = 354 nm λ= 420 – 660 nm Sample ND:YAG Laser OPO Dolf Timmerman Room-temperature Van der Waals-Zeeman Institute | University of Amsterdam 5 ns 10 Hz Spectro-meter Amsterdam Master of Physics Symposium 2008

  6. PL measurements Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam PL Si-NC Amsterdam Master of Physics Symposium 2008

  7. Photoluminescence Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam Time integrated PL-spectrum Amsterdam Master of Physics Symposium 2008

  8. Erbium One photon in  one photon out SiO2:(Er3+ +Si NC) Si-NC Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam Er3+ • NC absorbs photon • Energy transfer to erbium • Erbium emits at 1.5 μm 1.5 μm Amsterdam Master of Physics Symposium 2008

  9. Energy transfer Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam Amsterdam Master of Physics Symposium 2008

  10. Photoluminescence Er3+ Time integrated erbium PL flux-dependence Rate equations: Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam In the linear regime: NEr NEr The nr. of emitted photons is proportional to σPL σPLis determined from PL intensity flux-dependence Amsterdam Master of Physics Symposium 2008

  11. Absorption Linear absorption Absorbed fraction: Absorbed photons: Emitted photons: Define relative quantum efficiency: I0 I1 Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam Amsterdam Master of Physics Symposium 2008

  12. Relative quantum efficiency (η) Q.E. for different wavelengths in visible and near UV. Dolf Timmerman • η is constant up to a certain photon energy threshold • For larger photon energies a second excitation mechanism takes place Van der Waals-Zeeman Institute | University of Amsterdam Amsterdam Master of Physics Symposium 2008

  13. Quantum Cutting detected with Er3+ Dolf Timmerman Si-NC Van der Waals-Zeeman Institute | University of Amsterdam Er3+ Er3+ 0.8 eV Amsterdam Master of Physics Symposium 2008

  14. Quantum Cutting detected with Er3+ Dolf Timmerman Si-NC Van der Waals-Zeeman Institute | University of Amsterdam Er3+ Er3+ 1 in 2 out Amsterdam Master of Physics Symposium 2008

  15. η for Er3+ • Two samples • Identical Er3+ concentration and NC size • Different NC concentration • lower NC concentration  larger average NC-Er3+ distance Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam The quantum cutting process is less efficient for sample with larger NC-Er3+ distance Amsterdam Master of Physics Symposium 2008

  16. Relative quantum efficiency (η) Q.E. for different wavelengths in visible and near UV. Dolf Timmerman • η is constant up to a photon energy threshold of ≈ 2Eg • For larger photon energies quantum cutting takes place. Van der Waals-Zeeman Institute | University of Amsterdam Amsterdam Master of Physics Symposium 2008

  17. Quantum cutting with Si NCs Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam Eex < 2EG Eex > 2EG Space-separated quantum cutting (SSQC) Nature Photonics 2, 105-109 (2008) Amsterdam Master of Physics Symposium 2008

  18. Conclusions • Si NCs can be used to split energy quanta • Erbium ions and neighboring NCs are used to detect this • Space separation in NCs gives long lifetime of excitons, which is desired for applications Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam Amsterdam Master of Physics Symposium 2008

  19. Dolf Timmerman Van der Waals-Zeeman Institute | University of Amsterdam Amsterdam Master of Physics Symposium 2008

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