1 Carrier lifetime variations during irradiation by 3-8 MeV K in MCZ Si E.Gaubas 1, J.Vaitkus 1, A.Uleckas 1,J.Raisanen 2 Outline 1) Vilnius university, Institute of Materials Science and Applied Research, Vilnius, Lithuania (VU) 2) Helsinki University, Accelerator Laboratory group (HUAL) HUAL & VU instrumentation for lifetime measurement during proton irradiation, in-situ positioning and control Lifetime-temperature characteristics for initial MCz material and during irradiation with stopped and penetrative protons at different temperatures Summary
2 Motivavtion (ns) 10 4 Neutron irradiated material MCZ as-irradiated Proton irradiated material 10 3 sfz RT - 24 GeV/c DOFZ RT - 24 GeV/c It is interesting to understand: if this linear dependence is a result of irradiation or Fluence (cm -2 ) The dependence of the lifetime on the fluence in the neutron and proton irradiated Si. it is a consequence of irradiation and migration of defects to form other type of defects
3 Scheme of the installed instrumentation Modules outside irradiation area STA-01 laser driver Signal transfer lines C-C He Cryo Accelerator laboratory τ L =0.5 ns, E>10 μj Microchip SS laser MW oscillator VS P>20 mw, 22 GHz MW bridge FC adapter SMA/BNC 10 m Fiber guide MW waveguide MW waveguide MW coax Irradiation chamber Visual control & positioning system Positioning system Probes Sample VUTEG-3-HE MW detector Amplifier PC-NB for control of experiments Agilent 2C f 1 GHz, U 2 mv/pd, RL =50 Ω Visual control system LAN Master PC-NB cold finger, attached to C-C He Cryo The microwave probed photoconductivity (MW-PC) modules for the direct measurements of the carrier decay transients by employing MW absorption are assembled. VUTEG-3HE, master PC-NB, antenna/excitation fiber modules, positioning and visual control modules are installed within irradiation chamber containing a cold finger for cooling of a sample by using closed-cycle He cryostat. Delivering of signals to destination outside running irradiation area are implemented by using LAN.
4 Assembled instrumentation for τ-exposure-t measurements 3D positioning & inputs Drivers & and remote control instrumentation Distant transfer lines Beyond-radiation area & Measurement and operating instrumentation MW-PC signal MW needletip antenna and fiber probes Sample side for cross-sectional scan
5 τ-t measurements after irradiations HUAL in-chamber temperature control system Thermo-couple
6 τ-exposure at various T characteristics during irradiation with penetrative protons probes are located at half-width of wafer thickness MCZ Si irradiation is performed at: 50K 2 na 120K 2 na Variation of transients during irradiation (μs) Irradiation exposure time by 8 MeV protons (s) MCZ Si irradiation is performed at: 280K 4 na U MWR (V) MCZ Si 8 MeV protons irradiated at T = 50K Before irradiation 1 s irradiation 10 s 1E-3 0,01 0, t (μs) (μs) Irradiation exposure time by 8 MeV protons (s) U MWR (V) MCZ Si 8 MeV protons irradiated at T = 50K Before irradiation 1 s irradiation 10 s t (μs)
7 Irradiation of pre-irradiated Si 6 MeV protons current 1.5 na 0,5 1, MeV protons current 1.5 na (μs) MCZ Si 1E12 p/cm 2 pre-irradiated τ R (ns) Irradiation exposure (s) 0, Irradiation exposure (s)
8 τ-t results for initial material before irradiation mev 25 mev 32 mev τ (μs) MCZ Si 1/τ (μs -1 ) 17 mev 15 mev 75 mev τ ttr T (K) 19meV 92 K 68 K 60 K 200 K 122 K 0,005 0,0,015 0,020 1/T, K -1 Two-componential decay in the initial MCZ material wafers, ascribed to carrier recombination ( ) and trapping (τ ttr ), is observed, and these decay constituents show different temperature characteristics. For trapping constituent, a few peaks was be observed.
9 τ-t characteristics in the 8 MeV proton post-irradiated material Several carrier trapping components appear in τ-t characteristics after irradiation. Si 8MeV protons irradiated at T= 280K τ (μs) Si 8MeV protons irradiation at 50K τ tr-1 τ tr-2 τ (μs) E 4-58K E 5-110K 290 K -1 τ tr1-2 τ tr T (K) Si 8MeV protons irradiation at 50K T (K) -1 τ (μs) τ tr-2 42 mev τ tr-1 45 mev 0,005 0,0,015 0,020 0,005 0,0,015 0,020 1/T, K -1 1/T, K -1 τ (μs) 56 mev τ tr1-2 τ tr2-3
10 τ-exposure dependence during implantation of 3 MeV protons Microwave probe and optical fiber are located at ~ 80 μm distance from the irradiation (beam side) face-surface of wafer (μs) MCZ Si Irradiation is performed at : 280K 120K 50K 50K τ ttr Irradiation exposure time by 3MeV protons (s)
11 Summary The dependence of lifetime on fluence during irradiation by protons shows a dependence of defects generation rate on the temperature and of irradiation, i.e., irradiation itself induces the defect reactions in the sample. The pre-irradiation also creates the different conditions for defect reactions. (The increase of statistics is necessary) Two-componential decay in the initial MCZ material wafers, ascribed to carrier recombination ( ) and trapping (τ ttr ), is observed, and these decay constituents show different temperature characteristics. Several carrier trapping components appear in τ-t characteristics after irradiation by penetrative protons.
12 Thank You for attention! and Acknowledgements to Lithuanian Science and Studies Foundation, Ministry of Education and Science and to RD39 common fund for support of this work