1. Ultrafast carrier dynamics Optical Pump - THz Probe Ultrafast carrier dynamics in Br + -bombarded semiconductors investigated by Optical Pump - THz Probe spectroscopy Jean-Christophe DELAGNES jc.delagnes@cpmoh.u-bordeaux1.fr

2. April 2009 JPU 20092 Outline IntroductionIntroduction Experimental SetupExperimental Setup Samples preparationSamples preparation ResultsResults –InP –InGaAs PespectivesPespectives

3. April 2009 JPU 20093 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 How are the carrier lifetime and dynamics affected?Ionic irradiation: efficient method of engineering the carrier lifetime. How are the carrier lifetime and dynamics affected? Transient Terahertz Spectroscopic study of the effect of Br + irradiation of InGaAs and InP on the carrier lifetime and mobilityPresent study: Transient Terahertz Spectroscopic study of the effect of Br + irradiation of InGaAs and InP on the carrier lifetime and mobility Introduction Setup Samples Results Pespectives

4. April 2009 JPU 20094 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

5. April 2009 JPU 20095 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

6. April 2009 JPU 20096 Experimental Setup Pump: =810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump- Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Low excitation experiment: few µJ/pulse – w 0 ~2mm Initial carrier concentrations: 10 16 <n 0 <10 18 cm -3 Setup in vacuum box to prevent water absorption Introduction Setup Samples Results Pespectives

7. April 2009 JPU 20097 Experimental Setup Pump: =810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump- Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Low excitation experiment: few µJ/pulse – w 0 ~2mm Initial carrier concentrations: 10 16 <n 0 <10 18 cm -3 Setup in vacuum box to prevent water absorption Introduction Setup Samples Results Pespectives Optical Rectification (‘0’ frequency DFG)  (2) ( ,  ;  ~0) E THz (t)  I opt (t)

8. April 2009 JPU 20098 Experimental Setup Pump: =810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump- Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Low excitation experiment: few µJ/pulse – w 0 ~2mm Initial carrier concentrations: 10 16 <n 0 <10 18 cm -3 Setup in vacuum box to prevent water absorption Introduction Setup Samples Results Pespectives

9. April 2009 JPU 20099 Experimental Setup Pump: =810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump- Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Low excitation experiment: few µJ/pulse – w 0 ~2mm Initial carrier concentrations: 10 16 <n 0 <10 18 cm -3 Setup in vacuum box to prevent water absorption Introduction Setup Samples Results Pespectives  E THz (t): Transient modifications of E THz (t) (waveform) are recorded in time for different pump-probe delays EquilibriumPhotoexcitationRelaxation Scattering

10. April 2009 JPU 200910 Experimental Setup Pump: =810 nm (fs, CPA) Probe: Broadband (ps) THz Collinear Pump- Probe Geometry: Ultimate Temporal Resolution (limited only by the detector response)<ps Low excitation experiment: few µJ/pulse – w 0 ~2mm Initial carrier concentrations: 10 16 <n 0 <10 18 cm -3 Setup in vacuum box to prevent water absorption Introduction Setup Samples Results Pespectives

11. April 2009 JPU 200911 Samples Preparation 11 Mev Br + ions: deep implantation Introduction Setup Samples Results Pespectives [Br] [def]

12. April 2009 JPU 200912 Samples Preparation 11 Mev Br + ions: deep implantation Bulk InP Introduction Setup Samples Results Pespectives [Br] [def] Stopping Range of Ions in the Matter

13. April 2009 JPU 200913 Samples Preparation 11 Mev Br + ions: deep implantation Etched InP Introduction Setup Samples Results Pespectives [Br] [def]

14. April 2009 JPU 200914 Samples Preparation 11 Mev Br + ions: deep implantation InGaAs Introduction Setup Samples Results Pespectives [Br] [def]

15. April 2009 JPU 200915 InP: Results Slow Samples Transient modifications of the peak in the THz waveform vs. Pump-Probe delay  p (1D Scan). Spectrally averaged (unresolved) information about the carrier lifetime  c Time Resolved detection of the Terahertz waveform: Complex spectrum (Real & Imag. part) of the surface conductivity InP Introduction Setup Samples Results Pespectives

16. April 2009 JPU 200916 InP: Results Slow Samples Surface conductivity InP Introduction Setup Samples Results Pespectives

17. April 2009 JPU 200917 InP: Results Fast Samples FT along time FT along pump-probe delay Time dependent spectrum 2D spectrum Dynamics in 10 11 and 10 12 cm -2 samples is very fast (no quasi-dc analysis)  2D Fourier transformation provides a proper deconvolution H. Němec, et al., J. Chem. Phys. 122, 104503 (2005) Time Dependent Waveforms InP Introduction Setup Samples Results Pespectives

18. April 2009 JPU 200918 InP: Results Fast Samples InP Experimental 2D spectrum of the surface conductivity Drude model Fit Residuum exhibits no features GOOD AGREEMENT WITH A DRUDE MODEL Introduction Setup Samples Results Pespectives

19. April 2009 JPU 200919 InP: Results Power Dependence Shockley-Read model Large pump spot: No transverse diffusion InP Introduction Setup Samples Results Pespectives Phys. Rev. B, 78, 235206 (2008)

20. April 2009 JPU 200920 InP Results: Summary Sample n IRRAD (cm –3 )n Br (cm –3 )n 0 (cm –3 )  s (fs)  0 (cm 2 V –1 s –1 )  decay (ps) B9 2×10 16 01.6×10 17 1403000490 E9 9×10 16 5×10 12 1.1×10 17 120260070 B10 2×10 17 01.6×10 17 1202700100 E10 9×10 17 5×10 13 0.9×10 17 10021005.5 B11 2×10 18 01.6×10 17 7016002.6 E11 9×10 18 5×10 14 2.2×10 17 9021001.2 B12 2×10 19 01.6×10 17 409000.29 Influence of Br + ion concentration on Bulk and Etched sample parameters 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) InP Introduction Setup Samples Results Pespectives

21. April 2009 JPU 200921 InGaAs: Results Slow Samples Dose (cm –2 )  s (fs)  c (ps)  R/R (ps)  0,THz  0,Hall (cm 2 V –1 s -1 ) 10 9 0.25297 ± 5>500 (*) 260010800 10 0.2243± 5102100 -- 10 11 0.1753.4± 2<0.419004300 InGaAs (*) undoped Introduction Setup Samples Results Pespectives Single Component

22. April 2009 JPU 200922 In 1-x Ga x As: Results Fast Samples InGaAs (x=0.47) Conductivity: Sum of several contributions (3 paths) Introduction Setup Samples Results Pespectives Excitation Ground state State 2 (L-valley) State 1 (   -valley)  c,1  23  c,2 Drude response (  s,2 ) State 3 (  -valley)  c,3  13  12  21 Fit of the 2D spectrum gives access to the  ’s

23. April 2009 JPU 200923 In 1-x Ga x As Dynamics InGaAs (x=0.47) m L = 0.29 m e m X = 0.68 m e Introduction Setup Samples Results Pespectives m  = 0.041 m e

24. April 2009 JPU 200924 In 1-x Ga x As Dynamics InGaAs (x=0.47) m L = 0.29 m e m X = 0.68 m e Introduction Setup Samples Results Pespectives m  = 0.041 m e

25. April 2009 JPU 200925 In 1-x Ga x As Dynamics InGaAs (x=0.47) m L = 0.29 m e m X = 0.68 m e Introduction Setup Samples Results Pespectives m  = 0.041 m e

26. April 2009 JPU 200926 In 1-x Ga x As Dynamics InGaAs (x=0.47) m L = 0.29 m e m X = 0.68 m e Introduction Setup Samples Results Pespectives m  = 0.041 m e … and further slow relaxation …

27. April 2009 JPU 200927 In 1-x Ga x As Dynamics InGaAs (x=0.47) m L = 0.29 m e m X = 0.68 m e Introduction Setup Samples Results Pespectives m  = 0.041 m e … Somehow complicated … Improvement of the theoretical model by S.E.Ralph et al, Phys. Rev. B 54, 5568

28. April 2009 JPU 200928 Conclusion Time-resolved THz spectroscopy in Br + -bombarded : InP & In 0.53 Ga 0.47 As Characterization of : Lifetime & Mobility For  density of induced defects (not [Br + ]) both Lifetime and Mobility  InP (Most irradiated): carrier lifetime  3 orders of magnitude only reduced by factor 3mobility of carriers only reduced by factor 3 (vs. as-grown sample) trappingdiffusioncarrier trapping and carrier diffusion In 1-x Ga x As: As found in InP, both electron mobility and lifetime are reduced Very high photoexcited mobilityVery high photoexcited mobility 3600 cm 2 V –1 s –1 + 460 fs lifetime High potentialTHz optoelectronic  1.5 µmChanging 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  1.5 µm

29. April 2009 JPU 200929 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

30. April 2009 JPU 200930 Subpicosecond Non Contact Ohmmeter

31. April 2009 JPU 200931 Acknowledgments CPMOH Sample preparation, dc and optical characterisation Experiment hosted in Prag Support for international exchange E.N’Guema, L.Canioni, P.Mounaix H.Němec, L.Fekete, F.Kadlec, P.Kužel M.Martin, J.Mangeney

32. Thank you for your attention