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E.Gaubas, J.Vaitkus, T. Č eponis, A.Uleckas, J.Raisanen, S.Vayrynen, and E.Fretwurst

Fluence dependent recombination lifetime in neutron and proton irradiated MCz , FZ and epi-Si structures. E.Gaubas, J.Vaitkus, T. Č eponis, A.Uleckas, J.Raisanen, S.Vayrynen, and E.Fretwurst. Vilnius U niversity, Institute of Materials Science and Applied Research

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E.Gaubas, J.Vaitkus, T. Č eponis, A.Uleckas, J.Raisanen, S.Vayrynen, and E.Fretwurst

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  1. Fluence dependent recombination lifetime in neutron and proton irradiated MCz , FZ and epi-Si structures E.Gaubas, J.Vaitkus, T.Čeponis, A.Uleckas, J.Raisanen, S.Vayrynen, and E.Fretwurst Vilnius University, Institute of Materials Science and Applied Research HelsinkiUniversity, Accelerator Laboratory University Hamburg • Outline • Objectives of investigations • Samples, irradiations and experiments • Fluence dependent lifetime variations • Characteristics of lifetime cross-sectional profiles • Summary

  2. Objectives / investigations • Direct measurements of recombination lifetime fluence dependences: •  comparative analysis of carrier decay in MCZ, FZ and epi-Si neutron irradiated structures • Control of possible anneal of defects: • heat treatments 80C • Recombination lifetime variations with energy of protons • Recombination characteristics in 2 MeV proton irradiated n-FZ Si • combined investigations of MWR, DLTS and RR in 2MeV proton irradiated structures • - Cross-sectional scans within structure depth to control defect production profiles

  3. Diodes |2 MeV=7 m Structures tested 1.9 and 2.0 MeV protons Wafer structures =41-49 m M 1 2 Samples FZ WODEAN n- epi Neutron irradiated p- epi Proton irradiated FZ n-Si VU-HUAL Mesaurements: MW-PCD, RR, C-DLTS

  4. Neutron fluence dependent recombination lifetime in FZ and epi- Si

  5. Lifetime in neutron irradiated Si under heat treatments at 80C

  6. Fluence dependent lifetime variations in different particle energy irradiated structures

  7. 1.9 and 2.0 MeV protons =41-49 m Wafer structures Reff 20 mm 20 mm Lateral lifetime variation

  8. MW-PCD-depth – scans in 2 MeV protons irradiated FZ n-Si

  9. MW coaxial needle-tip antenna fiber sample Cross-sectional scans within depth of neutron irradiated wafer

  10. Fluence dependent variations of MW-PCD, DLTS and RR characteristics in 2 MeV protons irradiated FZ n-Si

  11. SUMMARY • Lifetime decreases from few s to about of 200 ps with enhancement of neutron irradiation fluence ranging from 1012 to 31016 n/cm2, as measured directly by exploiting microwave probed photoconductivity transients and verified by dynamic grating technique. • Lifetime values are nearly the same for neutron irradiated wafer and diode samples. These values are close to that in >20 MeV proton irradiated various Si diodes. • Small increase of lifetime values under annealing can be implied. • Lifetime values are nearly invariable within wafer thickness for high energy neutrons, while the lifetime depth profile is inhomogeneous for 2 MeV protons irradiated structures. • Production of recombination defectsin ~2 MeV protons irradiated FZ Si is efficient, and lifetime depth profiles correlate with stopping range of particles.

  12. Thank You for attention!

  13. Clusters PD V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 V2 Fluence

  14. Microwave probed photoconductivity (MW-PCD) in MW reflection mode (MWR) MWR >100m  0 =(4/c )dc, transient: (t)   (t) FC nexFC (t) (t) E.Gaubas. Lith. J. Phys., 43 (2003) 145. The microwave probed photoconductivity (MW-PCD) technique is based on the direct measurements of the carrier decay transients by employing MW absorption by excess free carriers. Carriers are photoexcited by 1062 nm light generated by pulsed (700 ps) laser and probed by 22 GHz cw microwave probe. Measurement techniques and instruments Dynamic gratings (DG) K.Jarasiunas, J.Vaitkus, E.Gaubas, et al. IEEE Journ. QE, QE-22, (1986) 1298. Diffraction efficiency (=I-1/I0) on light induced dynamic grating is a measure  (N)2of excess carrier density, while its variations in time (t)  exp(-2t/G) by changing a grating spacing () enable one to evaluate directly the parameters of grating erase 1/G = 1/R + 1/D through carrier recombination (R) and diffusion D = 2/(42D) with D as a carrier diffusion coefficient.

  15. MW instruments at VU Lateral mapping Cross-sectional scan

  16. Recombination lifetime in wafer and diode samples measured by MWR

  17. Neutron fluence dependent recombination lifetime in MCZ Si • R  t|U ~exp(-1) • R  gexcRs/gexcRL (UMWRs<2 ns /UMWRL>5 ns) Combined direct techniques

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