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 Astronomy2Department of Electrical Engineering and Computer Science

Vanderbilt University, Nashville, TN 37235 USA

2006 MURI Review – June 13, 2006

Support: DoD, AFOSR

Matthew J. Beck

MURI Review, June 2006

Non-Ionizing Energy Loss (NIEL)

Dale, et al. IEEE Trans. Nucl. Sci., v. 35 p. 1208

(1988).

Matthew J. Beck

MURI Review, June 2006

Experimental Results: Low-NIEL Irradiation

p- and n-Si divergence?

(1965)

(1965)(1965)

G.P. Summers, et al., 1993.

Dec

reas

e in

Min

ority

C

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r Diff

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n Le

ngth

Matthew J. Beck

MURI Review, June 2006

Low-NIEL Displacement Damage

NIEL

Low-NIEL

Srour, Marshall and Marshall. IEEE Trans. Nucl. Sci., v. 50 p. 653

(2003).

Matthew J. Beck

MURI Review, June 2006

Displacement Damage

Vacancy + Interstitial = Frenkel Pair (FP)

Matthew J. Beck

MURI Review, June 2006

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

Matthew J. Beck

MURI Review, June 2006

Method Details• Parameter-free DFT-LDA calculations

• Ultrasoft pseudopotentials

• Periodic boundary conditions

Matthew J. Beck

MURI Review, June 2006

Results: Equilibrium Properties

yx xz yz

Hexagonal

Tetragonal

+

Interstitial

VacancyApproximate

band of metastable FPs

5.4 Å

Matthew J. Beck

MURI Review, June 2006

Results: Electronic Structure

Valence Band

Conduction Band

Vacancy

Interstitial (~Tet)Frenkel Pair

0.38 nm

V0d2d I0

tet

Matthew J. Beck

MURI Review, June 2006

Results: Charge State Dependent Stability

Valence Band

Conduction Band

Fermi level

p-doped: FP+ is more

stable

Fermi level pinning by n- or p- type doping

n-doped: FP- is less

stable

Matthew J. Beck

MURI Review, June 2006

Analysis: Low-NIEL Defect Profiles

defectsn

Larger defect complexes, requiring large displacements

Effective defect “size”, or Displacement energy required to produce defect

Stable, Isolated FPs

p-Si

Intrinsic Si

n-Si

⇒ Opposite trend to experiments!

Matthew J. Beck

MURI Review, June 2006

Analysis: Frenkel Pair “Capture, Recombine, and Release” Mechanism

Stable FP in Si plus Conduction Band electron

Destabilized FP after electron

capture

Defect-less Si plus Conduction Band electron

FP

e-Si

Removal of excess electron carriersparticipating in this mechanism is delayed!

⇒ Measured excess carrier lifetimes are increased!

Matthew J. Beck

MURI Review, June 2006

Analysis: Effect of Increasing NIEL

defectsn

Increasing NIEL:

Effective defect “size”, or Energy required to produce defect

Larger defect complexes

Isolated FPs

Matthew J. Beck

MURI Review, June 2006

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

Matthew J. Beck

MURI Review, June 2006

Conclusions

• Low-NIEL irradiations: p-Si and n-Si divergence.

• Increasing NIEL: difference disappears.

Dec

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Matthew J. Beck

MURI Review, June 2006

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

Matthew J. Beck

MURI Review, June 2006

Experimental SetupAdapted Open Circuit Voltage Decay measurements for carrier lifetimes

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 Astronomy2Department of Electrical Engineering and Computer Science

Vanderbilt University, Nashville, TN 37235 USA

2006 MURI Review – June 13, 2006

Support: DoD, AFOSR