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Annealing of the vacancy-oxygen and divacancy-oxygen complexes in silicon

Annealing of the vacancy-oxygen and divacancy-oxygen complexes in silicon. M. Mikelsen 1 , E. V. Monakhov 1 , J. H Bleka 1 , J. S. Christensen 1 , B. S. Avset 2 , J. Härkönen 3 , B. G. Svensson 1 1 Department of Physics, Physical Electronics, University of Oslo, P.O. Box 1048 Blindern,

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Annealing of the vacancy-oxygen and divacancy-oxygen complexes in silicon

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  1. Annealing of the vacancy-oxygen and divacancy-oxygen complexes in silicon M. Mikelsen1, E. V. Monakhov1, J. H Bleka1, J. S. Christensen1, B. S. Avset2, J. Härkönen3, B. G. Svensson1 1Department of Physics, Physical Electronics, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo, Norway 2SINTEF, Electronics and Cybernetics. P.O. Box 124 Blindern, N-0314 Oslo, Norway (Present address: Statens Strålevern, Grini næringspark 13, POB 55, 1332 Østerås) 3Helsinki Institute of Physics, Helsinki University, Helsinki, Finland Special thanks to: The Norwegian Research Counsel (NFR) for Financial Support

  2. Background During irradiation we get: V + Oi VO V + V  V2 (V2 is also produced directly) For higher doses: V + VO  V2O Another channel for V2O formation: V2 + Oi V2O Basis for I-level identification Basis for X-level identification

  3. Background • X was identified as V2O • V2 migrates: • V2 + Oi V2O M. Mikelsen, E. V. Monakhov, G. Alfieri, B. S. Avset, and B. G. Svensson Phys. Rev. B 72, 195207 (2005)

  4. Experiment Survey of the samples used in the study: 6 MeV electrons • DOFZ = Diffusion-Oxygenated Float-Zone Si • MCZ = Magnetic Czochralski • Experimental method: • DLTS • Pre-annealing to insure a V2 V2O transformation. • Isothermal annealing in the range 275-355 oC. Dose: 2 - 5 ×1012 cm-2

  5. Results: DOFZ - Si

  6. Results: DOFZ - Si • Other levels observed: • A at ~157 K (*) • B at ~200 K • Similar electrical parameters as V2O(-/0). • C at ~175 K • D at ~157 K • (*) To be discussed in: • ”On the formation of the L-center in silicon during heat treatment in the temperature range 205 to 285°C” • M. Mikelsen, E. V. Monakhov, B. S. Avset, B. G. Svensson • To be published in “Physica sicripta”

  7. Results: DOFZ - Si • The activation enthalpies for peak C and D were obtained by using a computer program that fits the spectrum to a sum of single peaks.

  8. Results: MCZ Si • MCZ-Si behaves similar to DOFZ • But the area between the two V2O peaks looks a little bit different. (No D-peak)

  9. Results: V2O annealing • The annealing of V2O(=/-) exhibits first order kinetics. • For both MCZ and DOFZ. • For all annealing temperatures in the range 275 - 355 oC. • The kinetics for V2O(-/0) is affected by overlapping level. Example:

  10. Results: V2O annealing

  11. The V2O annealing mechanism • It is improbable that V2O anneals by migration and trapping. • Since Oi is the main impurity, one would expect V2O2 to form. • V2O2 is believed to be electrically active with two acceptor centers similar to V2 andV2O. • V2O does not anneal by interacting with migrating oxygen dimers. • The diffusivity of O2 is to low by a factor 104.

  12. The V2O annealing mechanism • A prefactor, c0, in the 1012 – 1013 range is expected for dissociation. • The experimental value is in this range taking in regard the uncertainty. • If dissociation were to occur we would expect an increase in VO; V2O  V + VO …. So we must investigate the VO annealing, to check if it really is dissociation.

  13. Results: VO annealing (DOFZ) • After the initial increase, [VO] decreases with 1st. order kinetics.

  14. A model for defect annealing • The reactions • V2O  VO +V (dissociation) • V + Oi  VO (migration of V) • VO + Oi  VO2 (migration of VO) • VO  V + Oi (dissociation) • VO +V  V2O (migration of V) • The diff-equations • d[VO]/dt = - Cdiss_V2O(T) [V2O] + 4 R DV(T) [V] [VO] • d[VO]/dt = Cdiss_V2O(T) [V2O] + 4 R DV(T) [V] [Oi] – 4 R DVO(T) [VO] [Oi] - Cdiss_VO(T) [VO] – 4 R DV(T) [V] [VO] • d[V]/dt = Cdiss_V2O(T) [V2O] + Cdiss_VO(T) [VO] – 4 R DV(T) [V] [Oi] - 4 R DV(T) [V] [VO]

  15. Results: VO annealing (DOFZ) • The model is highly sensitive to the [Oi] concentration. We used [Oi]= 2.5 x 1017.

  16. Results • Hydrogen may interact with VO.

  17. Summary • The V2O defect anneals with an activation energy, Ea, of ~2.0 eV and a prefactor ~2 x 1013 s-1. • Dissociation is the likely annealing mechanism for V2O. • A model that includes VO and V2O dissociation and VO migration and trapping describes the observed annealing kinetics well.

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