1 / 12

Recent related paper: Solid State Phenomena, 178-179 (2011) 313

Positron Annihilation on Point Defects in n-FZ –Si:P Single Crystals Irradiated With 15 MeV Protons (or what has been observed beyond expectations) N. Yu. Arutyunov 1,2 , M. Elsayed 1 ,R. Krause-Rehberg 1 , 1 Department of Physics, Martin Luther University, 06120 Halle, Germany

wyman
Download Presentation

Recent related paper: Solid State Phenomena, 178-179 (2011) 313

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Positron Annihilation on Point Defects in n-FZ –Si:P Single Crystals Irradiated With 15 MeV Protons (or what has been observed beyond expectations) N. Yu. Arutyunov1,2, M. Elsayed1,R. Krause-Rehberg1, 1Department of Physics, Martin Luther University, 06120 Halle, Germany 2 Institute of Electronics, Tashkent 700170, Uzbekistan V.V. Emtsev3,G.A. Oganesyan3 ,V.V. Kozlovski4 3Ioffe Physico-Technical Institute, St. Petersburg 194021, Russia 4St. Petersburg State Polytechnic University ,St. Petersburg 195251, Russia Recent related paper: Solid State Phenomena, 178-179 (2011) 313

  2. Which Defects Are Produced In n-FZ-Si([P]) Under Irradiation with 15 MeV Protons? ● Oxygen[O] ≈ 1016 cm-3, carbon lean[Ci]≈ 1015 cm-3, n-FZ-Si([P]=7×1015 cm-3) is of special interest because irradiation allows one to change position of Fermi level in wide range. Information about RD created in material is scarce. ●Most probable primary defects are separated Frenkel pairs, V and I; they are movable and they may create various complexes ● Established:Most probablesecondary defects aredivacancies (VV)and donor-vacancy pairs (or E-centers for D=P); ►Anticipated stagesof annealing of defects are completed at: 180°C (E-centers), 280°C(VV)(EPR, DLTS, Hall’s measurements)

  3. What we hoped to obtain creating defects in n-FZ-Si([P]) under irradiation with 15 MeV protons? We hoped to optimize parameters of irradiation/annealing Goal:to control reliably the position of the Fermi level creating E-centers and divacancies We expectedto reach the goal combining isochronal annealing and dose of irradiation Results of annealing surpass all expectations! E (P+)=15 MeV 0,8 mm Si E (P+)=8 MeV Projection range of protons > 1 mm: no stoppage effects ● Slowing down of protons+is due to ionization lost: roughly, average ionization energyI ≈ 172 eV, energy of recoil atomER: 210 eV Generation of vacancies and interstitials dominates

  4. Characterization: Hall’s measurements and removal Of CarriersFrom Conduction Band of n-FZ-Si([P]) Irradiated with 15 MeV Protons (Hall’s measurements) ● Removal rate of electrons: ≈ 110–120 cm-1 (15 MeV H+) and ≈ 0,11 cm-1 (1 MeV electrons)►tecnological advantage of H+ beams ● Concentration of defects has been estimated using these data; Values have been applied for analysis of results obtained by PALS

  5. Temperature Dependency of e+ Lifetime Inn-FZ-Si([P]) Irradiated with 15 MeV Protons ●τav , - strong T-dependency indicates effective positron-phonon interaction ● Value of e+ lifetime suggests defects of a vacancy type (~ 254 ps) ● Shallow e+ state (s): Est ≈ 0,2 – 0,6 meV (Krause-Rehberg, Leipner, 1999) ●We expected:E-centers, VV dominate, they are e+ traps► isochronal annealing must be completed at 280 °C – 300 °C ● We obtained: T- dependency is preserved up to Tann.=340 °C!

  6. Positron Lifetime And Recovery Of Dopant Activity:Deep Donors Of Radiation Origin Hidden At Early Stages of Annealing Of n-FZ-Si([P]) Irradiated With 15 MeV Protons: ● e+ lifetime ~251 ps is steady up to ~ 320°C, then its recovery begins ●E-centers, VVannealed, ~ 35-40% of atoms of Prestored electrical activity ● At 500°C:e+ lifetime vanishes, recovery of electrical activity of atoms of P continues up to 700 °C ●We identify thermally stablee+ trapsas deep donorshidden in early stages of annealing

  7. Temperature Dependency Of Positron Trapping Rate For Deep Donors Of Radiation Origin In n-FZ-Si([P]) Irradiated With 15 MeV Protons ● For deep donors: reciprocal cubic temperature dependencyof e+trapping rate► multi-phonon cascade trappingat attractive center (Abakumov et al., 1978) ● e+Trapping cross-section (averaged over temperature)≈ 6,3×10-13 cm2for concentration of deep donors≈ 1015cm-3(Hall effect and conductivity)

  8. Activation Energy of Annealing Of Deep Donors Of Radiation Origin In n-FZ-Si([P]) Irradiated With 15 MeV Protons Equation of kinetics of chemical reaction (Arutyunov et al., 1977) ● Annealing ► 1st order of reactionγ=1►number of sinks is fixed, new e+traps are not formed ● Ea ≈ 0,74 eVcorresponds to data of EPR: Ea≥ 0,64 eV attributed to dissociation of VV in its neutral state (G.D. Watkins, 1964) ●k is e+trapping rate; λ0-1=τ0 ≈ 216 ps is e+ lifetime in the bulk; λav -1 = τavis e+lifetime at 30K; τd is maximal value of τav

  9. Number of Vacancies In Deep Donors Of Radiation Origin In n-FZ-Si([P]) Irradiated With 15 MeV Protons ● Average e+ lifetime τav overlaps the range of numbers of vacancies in the cluster from 1 to 2 ● Long-lived τav lifetime is in the range of numbers of vacancies from 2 to 3 ● Resume: deep donor contains more than 1 vacancy (most probably: 2 vacancies) ●Black squares: calculations, Hakala et. al, PRB,1998

  10. Formal configuration of deep donordetected in n-FZ-Si ([P]) irradiated with protons 15 MeV ●Two vacancies are in close proximity to atom of P ●Atoms of silicon participate in the closing of bonds ● Decomposition of deep donorrestores impurity atom of P as a shallow donor Relaxation is not shown

  11. Conclusion • ● Deep donorsof radiation origin have been revealed in silicon of n-type conductivity • (n-FZ-Si([P]),irradiated with 15 MeV protons) • ● Data of e+ lifetime: • Configuration of deep donor consists of 2vacancies; • it includes, at least, one atomof phosphorus • ●Anealing of deep donors ranges 320°C to 700°C • Deep donors are hiddenin stages of annealing of well known E-centers and divacancies • (ii) Deep donor is effective trap of e+:σ ≈ 6,3×10-13 cm2 • ●Good electron wave functions are needed(to shed the light on details of configuration of deep donor)

  12. Defects In n-FZ-Si([P]) Single Crystal Irradiated With 15 MeV Protons: Why We Applied PALS? ●Sensitivity of the positron lifetime to vacancy defects and their complexes with atoms of dopant (P) Difficulties in EPR studying of E-center and VV: ►Absence of EPR signal for negatively charged phosphorus-vacancy complex (E-center) ● Insensitivity of EPR signal in the process of isochronal annealing to the charge state of divacancy (VV1+ and VV1–) ●Necessity to assume the existence of the intermediateneutral state of VV which is undetectable by EPR; energy of dissociation of VV0 ≈ 0,64 eV(G.D. Watkins, 1964)

More Related