1. ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ Manuel Forcales

2. OPTICAL MEMORY EFFECT IN Si:Er ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ Free Electron Laser facility for Infrared eXperiments (FELIX) &

3. Acknowledgements Group members from the Van der Waals–Zeeman Institute (WZI): M. A. J. Klik, N.Q. Vinh, Dr. M. Wojdak and Dr. T. Gregorkiewicz FOM Institute “Rijnhuizen” (FEL Facility) staff members: Dr. I. Bradley, Dr. J-P.R. Wells Samples kindly provided by: Dr. A. Polman, AMOLF, The Netherlands Dr. Widdershoven, PRL, The Netherlands Dr. F. Priolo, IMETEM, Italy Dr. W. Jantsch, University of Linz, Austria Dr. J. Michel, MIT, USA Financial support (thank$): ARL-ERO, NWO, FOM _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

4. Outline     Motivations Photoluminescence (PL) experiments Results Conclusions _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________  Introduction: data storage/Er 3+ excitation

5. Intro I: Optical data storage _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ Need for all-optical data storage  writing, reading and erasing by photons ... write read electronics CD Process of writing  Thermal in nature (melt, cool down) All optical process  FAST Approaches: - Holographic optical storage (IBM, Lucent) - Hole burning Optical memory effect observed in III-V semicond., but never in Si

6. Motivation for using Si _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ Why Si? King of electronics Environmentally friendly Environmentally friendly Total control of dopants Total control of dopants potential for photonics?  potential for photonics? (Integration of electronics and photonics, on-chip)   

7. Motivation for using erbium (Er) _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ Why Er? Are there other rare earth (RE) elements available?  Are there other rare earth (RE) elements available?     Inner 4f-electron shell transitions Emission at 1.54  m (telecommunications) Sharp transitions in wavelength Almost independent of host material

8. Silicon doped with rare earths Ce 3+ Pr 3+ Nd 3+ Pm 3+ Sm 3+ Eu 3+ Gd 3+ Tb 3+ Dy 3+ Ho 3+ Er 3+ Tm 3+ Yb 3+ RE ground state Si bandgap _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

9. Er 3+ excitation in an insulator (SiO 2 ) _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ Er 3+ ion Direct Er 3+ excitation  10 -21 cm -2 All erbium can be excited OPTICALLY Er PL @ 1.54  m We need laser to pump Er. We need resonant energies. ELECTRICALLY Electron impact excitation  10 -14 cm -2 LED with quantum efficiencies  10 % (similar to III-V semicond.) STMicroelectronics “New York Times, Oct. 2002 ” Patent by STM  Er  12 ms nc-Si Solution ? Use sensitizers like nc-Si BAD ! EDFA

10. Optical Er 3+ excitation sensitized with nc-Si _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ Er nc-Si Current investigations are based on: - Excitation spectroscopy (power and wavelength dependence)  CW or pulsed - Kinetics (rise time, decay time), temperature dependence… Dr. Wojdak ;-) How many optically active Er?, Excitation cross section?, Excitation/ Energy transfer mechanism?, Possibility to obtain GAIN? Er

11. Optical Er 3+ excitation in crystalline Si Indirect excitation   10 -15 cm -2  increased 6 orders of magnitude ! Generation of carriers optically  band-to-band excitation E > E gap (1170 meV) (also possible electrically) Er 3+ ion Nd:YAG VB CB Er-related allows recombination level (electron and hole)  Er 3+ excitation Role of shallow traps excitation / de- excitation?  Mid infrared radiation Source  FREE ELECTRON LASER Er-related _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________  Er  1 ms

12. Er 3+ de-excitation in crystalline Si Back-transfer  Provided by  E (thermally or by FEL ) Ionization of traps may induce excitation or Auger de-excitation Er 3+ ion VB CB Er-related _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ +E+E Thermal effects quench completely RT emission at 1.54  m  Thermal effects quench completely RT emission at 1.54  m Er 3+ ion Energy migration Er 3+ ion Up-conversion  > E gap

13. Free Electron Laser (FEL) facility High brilliance and precise energy tuning: (70-170) meV The magnetic field generates periodically curved electron trajectory _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ The induced oscillating dipole moment leads to emission of radiation

14. Photoluminescence experimental set-up T = 4.2 K sample Ge / PMT emission @ 1.54  m Spectrometer Follow changes in: - Spectrum - Amplitude - Kinetics Tunable delay time (  t) and variable power Nd:YAG (532 nm) FEL (10  m ) tt _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

15. Experimental set-up (real one) _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

16. Er ions implanted: energy: 300 keV dose: 3*10 12 cm -2 Er-concentration: 5*10 17 cm -3 Oxygen ions co-implanted: energy: 40 keV dose: 3*10 13 cm -2 annealing: 900 o C (N2 atmosphere) time: 30 minutes. Intensity Wavelength (nm)  1.5  m Time (ms) Intensity at 1.5  m   1 ms Photoluminescence of Si:Er _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

17. Afterglow and Er PL enhancement Er PL Nd:YAG FEL  afterglow  100-150 ms 4.2 K _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ No effect when FEL is fired before Nd:YAG

18. Dynamics of the enhancement effect  afterglow   enhancement M. Forcales et al., Phys. Rev. B 65, 195208 (2002) _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

19. Model VB CB Er 3+ matrix Nd:YAG, Ar + FEL Er-related level Er PL _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

20. Temperature dependence _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

21. Single carrier excitation Enhancement effect does not follow ( I FEL ) 2, quadratic dependence Er 3+ ion VB CB Er-related I FEL Incorrect Model M. Forcales et al., Phys. Rev. B 67, 0853xx (2003) _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

22. MIR photon flux Enhancement amplitude FEL = 14  m fits the trap-ionization dependence: p = (-I  I +sqrt(I 2  I 2 +4  I  c I  N tr ))/2  c Dependence on flux _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________ Ionization of traps Enhancement has a  dependence related to one carrier excitation

23. Concept of a Si-based optical storage element Storage arrayStorage element Writing beam λ 1 (band-to-band) Recovered signal at 1.54  m Reading beam λ 2 (below band gap) M. Forcales et al., Solid State Electronics, vol. 47, 165 (2003) _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

24. Futures perspectives - Need to improve thermal stability! How? Using deeper acceptor traps (Zn, Mg). -No need to use free electron laser! How? Table-top OPO, CO 2 or cascade lasers… - Creation of electrons and holes separated in time! How? Prepare the system by proper injection of carriers. VB CB Er-related A tr Si-based optical elements could find applications in: - Telecommunication networks at 1.54  m - Optical storage devices for use in all-photonic technology - Quantum computing ?… _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________

25. Conclusions Observation of afterglow and optical memory effect in Si:Er system at temperatures T < 50 K The effect is a fundamental property of silicon (revealed by the optical dopant Er) Proper engineering, will allow long time storage and thermal stability  _____________________ Van der Waals-Zeeman Institute, University of Amsterdam ________________ ___________________________________________ Group meeting, Feb. 2003 _____________________________________________