Elemental Defect Processes in Radiation-Induced Displacement Damage in Si

1. Elemental Defect Processes in Radiation-Induced Displacement Damage in Si Matthew J. Beck1, R. Hatcher1, L. Tsetseris1, M. Caussanel2, R.D. Schrimpf2, D.M. Fleetwood2,1, and S. T. Pantelides1 1Department of Physics and Astronomy 2Department of Electrical Engineering and Computer Science Vanderbilt University, Nashville, TN 37235 USA 2006 MURI Review – June 13, 2006 Support: DoD, AFOSR

2. Non-Ionizing Energy Loss (NIEL) Dale, et al. IEEE Trans. Nucl. Sci., v. 35 p. 1208 (1988).

3. Experimental Results: Low-NIEL Irradiation p- and n-Si divergence? G.P. Summers, et al., 1993. Decrease in Minority Carrier Diffusion Length (1965) (1965) (1965)

4. Low-NIEL Displacement Damage NIEL Low-NIEL Srour, Marshall and Marshall. IEEE Trans. Nucl. Sci., v. 50 p. 653 (2003).

5. Displacement Damage Vacancy + Interstitial = Frenkel Pair (FP)

6. Introduction: First Principles and Frenkel Pairs • Frenkel Pairs (FPs) are… • Atomic scale, materials specific • Require atoms AND electrons (e.g. Jahn-Teller effects) • Can be modeled in “small” cell (~216 atoms) • First Principles methods are… • Atomic scale • Highly accurate for atoms AND electrons • Materials specific • BUT… limited to SMALL systems

7. Method Details • Parameter-free DFT-LDA calculations • Ultrasoft pseudopotentials • Periodic boundary conditions

8. Interstitial Vacancy Approximate band of metastable FPs Tetragonal + Hexagonal Results: Equilibrium Properties 5.4 Å

9. Vacancy Interstitial (~Tet) Frenkel Pair Results: Electronic Structure 0.38 nm Conduction Band V0d2d I0tet Valence Band => FP0 = V2- + I2+

10. n-doped: FP- is less stable p-doped: FP+ is more stable Results: Charge State Dependent Stability Conduction Band Valence Band Fermi level Fermi level pinning by n- or p- type doping

11. Analysis: Low-NIEL Defect Profiles Stable, Isolated FPs Larger defect complexes, requiring large displacements p-Si Intrinsic Si n-Si Effective defect “size”, or Displacement energy required to produce defect ⇒Opposite trend to experiments!

12. Destabilized FP after electron capture Defect-less Si plus Conduction Band electron Analysis: Frenkel Pair “Capture, Recombine, and Release” Mechanism FP e- Si Stable FP in Si plus Conduction Band electron Removal of excess electron carriers participating in this mechanism is delayed! ⇒ Measured excess carrier lifetimes are increased!

13. Analysis: Effect of Increasing NIEL Increasing NIEL: Larger defect complexes Isolated FPs Effective defect “size”, or Energy required to produce defect

14. Summary of Relevent Results:n- vs. p-type Behavior • Significantly more small, isolated Frenkel Pairs are expected in p-type Si than n-type Si. • Electron capture destabilizes these Frenkel Pairs, delaying the permanent removal of these minority carriers in p-Si. • For higher NIEL irradiations, the magnitude of this effect becomes insignificant

15. Conclusions • Low-NIEL irradiations: p-Si and n-Si divergence. • Increasing NIEL: difference disappears. Decrease in Minority Carrier Diffusion Length

16. Conclusions and Future Work • Elemental defect processes directly control larger-scale material and device behavior • First Principles calculations can reveal the rich physics associated with fundamental defects • Future Work: • Separation/Recombination Dynamics • Electronic Structure => Internal Charge transfer • Experimental Validation of Mechanism

17. Experimental Setup Adapted Open Circuit Voltage Decay measurements for carrier lifetimes

18. Elemental Defect Processes in Radiation-Induced Displacement Damage in Si Matthew J. Beck1, R. Hatcher1, L. Tsetseris1, M. Caussanel2, R.D. Schrimpf2, D.M. Fleetwood2,1, and S. T. Pantelides1 1Department of Physics and Astronomy 2Department of Electrical Engineering and Computer Science Vanderbilt University, Nashville, TN 37235 USA 2006 MURI Review – June 13, 2006 Support: DoD, AFOSR