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Jean-Christophe DELAGNES jc.delagnes@cpmoh.u-bordeaux1.fr

Ultrafast carrier dynamics in Br + -bombarded semiconductors investigated by Optical Pump - THz Probe spectroscopy. Jean-Christophe DELAGNES jc.delagnes@cpmoh.u-bordeaux1.fr. Outline. Introduction Experimental Setup Samples preparation Results InP InGaAs Pespectives.

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Jean-Christophe DELAGNES jc.delagnes@cpmoh.u-bordeaux1.fr

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  1. Ultrafast carrier dynamicsin Br+-bombarded semiconductorsinvestigated byOptical Pump - THz Probespectroscopy Jean-Christophe DELAGNES jc.delagnes@cpmoh.u-bordeaux1.fr

  2. Outline • Introduction • Experimental Setup • Samples preparation • Results • InP • InGaAs • Pespectives JPU 2009

  3. Introduction & Motivations • Generation of coherent terahertz pulses in ultrafast semiconductors (LT-AsGa and other materials) • Specific methods aim to increase the concentration of traps: • Film growth and Doping • Implantation or Irradiation with heavy ions • Ionic irradiation: efficient method of engineering the carrier lifetime. How are the carrier lifetime and dynamics affected? • Present study: Transient Terahertz Spectroscopic study of the effect of Br+ irradiation of InGaAs and InP on the carrier lifetime and mobility Introduction Setup SamplesResults Pespectives JPU 2009

  4. Why using THz in SC science? • THz Radiation is indeed a valuable tool for (true) optoelectronics studies Electronics Gunn Diode p-i-n Diode High mobility transistor (HEMT) Optics NL Optics Ultrafast Lasers QCL JPU 2009

  5. Why using THz in SC science? • THz Radiation is indeed a valuable tool for (true) optoelectronics studies Electronics Gunn Diode p-i-n Diode High mobility transistor (HEMT) Optics NL Optics Ultrafast Lasers QCL JPU 2009

  6. Experimental Setup Pump: l=810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump-Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Introduction Setup SamplesResults Pespectives Low excitation experiment: few µJ/pulse – w0~2mm Initial carrier concentrations: 1016<n0<1018 cm-3 Setup in vacuum box to prevent water absorption JPU 2009

  7. Experimental Setup Optical Rectification (‘0’ frequency DFG) c(2)(w,-w;W~0) ETHz(t)Iopt(t) Pump: l=810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump-Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Introduction Setup SamplesResults Pespectives Low excitation experiment: few µJ/pulse – w0~2mm Initial carrier concentrations: 1016<n0<1018 cm-3 Setup in vacuum box to prevent water absorption JPU 2009

  8. Experimental Setup Pump: l=810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump-Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Introduction Setup SamplesResults Pespectives Low excitation experiment: few µJ/pulse – w0~2mm Initial carrier concentrations: 1016<n0<1018 cm-3 Setup in vacuum box to prevent water absorption JPU 2009

  9. Experimental Setup Pump: l=810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump-Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Introduction Setup SamplesResults Pespectives Equilibrium Photoexcitation Relaxation Scattering DETHz(t): Transient modifications of ETHz(t) (waveform) are recorded in time for different pump-probe delays Low excitation experiment: few µJ/pulse – w0~2mm Initial carrier concentrations: 1016<n0<1018 cm-3 Setup in vacuum box to prevent water absorption JPU 2009

  10. Experimental Setup Pump: l=810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump-Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Introduction Setup SamplesResults Pespectives Low excitation experiment: few µJ/pulse – w0~2mm Initial carrier concentrations: 1016<n0<1018 cm-3 Setup in vacuum box to prevent water absorption JPU 2009

  11. Samples Preparation 11 Mev Br+ ions: deep implantation [Br] [Br] Introduction Setup Samples Results Pespectives [def] [def] JPU 2009

  12. Bulk InP Samples Preparation 11 Mev Br+ ions: deep implantation [Br] [Br] Introduction Setup Samples Results Pespectives [def] [def] Stopping Range of Ions in the Matter JPU 2009

  13. Etched InP Samples Preparation 11 Mev Br+ ions: deep implantation [Br] [Br] Introduction Setup Samples Results Pespectives [def] [def] JPU 2009

  14. InGaAs Samples Preparation 11 Mev Br+ ions: deep implantation [Br] [Br] Introduction Setup Samples Results Pespectives [def] [def] JPU 2009

  15. InP InP: Results • Slow Samples Transient modifications of the peak in the THz waveform vs. Pump-Probe delay tp (1D Scan). Introduction Setup Samples Results Pespectives Spectrally averaged (unresolved) information about the carrier lifetime tc Time Resolved detection of the Terahertz waveform: Complex spectrum (Real & Imag. part) of the surface conductivity JPU 2009

  16. InP InP: Results • Slow Samples Surface conductivity Introduction Setup Samples Results Pespectives JPU 2009

  17. InP InP: Results • Fast Samples Dynamics in 1011 and 1012 cm-2 samples is very fast (no quasi-dc analysis)  2D Fourier transformation provides a proper deconvolution Time dependent spectrum Introduction Setup Samples Results Pespectives FT along time FT along pump-probe delay Time Dependent Waveforms 2D spectrum H. Němec, et al., J. Chem. Phys.122, 104503 (2005) JPU 2009

  18. InP InP: Results • Fast Samples Experimental 2D spectrum of the surface conductivity Introduction Setup Samples Results Pespectives Drude model Fit Residuum exhibits no features GOOD AGREEMENT WITH A DRUDE MODEL JPU 2009

  19. InP InP: Results • Power Dependence Introduction Setup Samples Results Pespectives Shockley-Read model Large pump spot: No transverse diffusion Phys. Rev. B, 78, 235206 (2008) JPU 2009

  20. InP InP Results: Summary Influence of Br+ ion concentration on Bulk and Etched sample parameters Introduction Setup Samples Results Pespectives • Carriers lifetime: • Due to density of induced defects • Not significantly influenced by Br implantation • Trapping time decreases by 3 orders of magnitude (Log) • Mobility decreases only by a factor 3 (Linear) JPU 2009

  21. InGaAs InGaAs: Results • Slow Samples Single Component Introduction Setup Samples Results Pespectives (*)undoped JPU 2009

  22. InGaAs t12 State 1 (G*-valley) State 2 (L-valley) t13 t21 t23 State 3 (G-valley) Drude response (ts,2) tc,1 tc,3 tc,2 Excitation Ground state In1-xGaxAs: Results (x=0.47) • Fast Samples Introduction Setup Samples Results Pespectives Conductivity: Sum of several contributions (3 paths) Fit of the 2D spectrum gives access to thet’s JPU 2009

  23. InGaAs In1-xGaxAs Dynamics (x=0.47) mL = 0.29 me mX = 0.68 me mG = 0.041 me Introduction Setup Samples Results Pespectives JPU 2009

  24. InGaAs In1-xGaxAs Dynamics (x=0.47) mL = 0.29 me mX = 0.68 me mG = 0.041 me Introduction Setup Samples Results Pespectives JPU 2009

  25. InGaAs In1-xGaxAs Dynamics (x=0.47) mL = 0.29 me mX = 0.68 me mG = 0.041 me Introduction Setup Samples Results Pespectives JPU 2009

  26. InGaAs In1-xGaxAs Dynamics (x=0.47) mL = 0.29 me mX = 0.68 me mG = 0.041 me Introduction Setup Samples Results Pespectives … and further slow relaxation … JPU 2009

  27. InGaAs In1-xGaxAs Dynamics (x=0.47) mL = 0.29 me mX = 0.68 me mG = 0.041 me Introduction Setup Samples Results Pespectives … Somehow complicated … Improvement of the theoretical model by S.E.Ralph et al, Phys. Rev. B 54, 5568 JPU 2009

  28. Conclusion Time-resolved THz spectroscopy in Br+-bombarded : InP & In0.53Ga0.47As Characterization of : Lifetime & Mobility For  density of induced defects (not [Br+]) both Lifetime and Mobility  InP (Most irradiated): • carrier lifetime  3 orders of magnitude • mobility of carriers only reduced by factor 3 (vs. as-grown sample) • carrier trapping and carrier diffusion In1-xGaxAs: • As found in InP, both electron mobility and lifetime are reduced • Very high photoexcited mobility 3600 cm2V–1s–1 + 460 fs lifetime • Changing x and [Br+] : large tunabilty of optical and electronic material parameters  Improvement of ultrafast optoelectronic devices based on this material. High potential for THz optoelectronic at l=1.5 µm JPU 2009

  29. Perspectives • Wavelength dependence: • Penetration depth / Initial profile • Electronic State • Temperature dependence • Clusters of defects • Automated Measurement: • Single shot waveform + pump-probe • Single shot 2D Introduction Setup Samples Results Pespectives JPU 2009

  30. Subpicosecond Non Contact Ohmmeter JPU 2009

  31. Acknowledgments • CPMOH • Sample preparation, dc and optical characterisation • Experiment hosted in Prag • Support for international exchange E.N’Guema, L.Canioni, P.Mounaix M.Martin, J.Mangeney H.Němec, L.Fekete, F.Kadlec, P.Kužel JPU 2009

  32. Thank you for your attention

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