Modeling of Helium Implantation in SiC

1
Modeling of Helium Implantation in SiC
Qiyang Hu, Shahram Sharafat, Nasr M. Ghoniem
University of California Los Angeles (UCLA)
Current Status of HEROs
New Phenomena in SiC
SiC Key Properties

• Experimental He-Implantation of SiC Chen, et.al.
  2000
• 26.3 MeV a-Beam
• 51 Al-Degrader Foils
• Uniform implantation to 200 mm
• Findings
• He radiation damage retained in SiC after
  annealing (1520 K) ? Dense population of bubbles
  and dislocation loops
• No visible damage occurs under the same
  conditions after He-free irradiation.
• After annealing 1520 K? Depleted zones along GB
  and inside grain 0.5 mm from GBs.
• No defects in grains smaller than 0.5 mm
• The DZs beneficial in SiC fibers with diameters
  below lt1 mm.
• Above 200 appm He in SiC faceted bubbles form
  along GBs annealing (gt1520 K).
• At RT 2450 appm He ? Platelets (9 nm diam. 0.6
  nm thick)
• At lower appm platelets visible only after
  annealing (1520 K)
• Above 1520 K with gt350 appm He, platelets break
  up into disks of bubbles
• Concurrently interstitial-type dislocation loops
  are formed,
• Bubbles and loops coarsen upon annealing by
  apparently strongly correlated coarsening
  processes.
• He platelets form gas-filled nanocracks.

Crystal Types
Defect Properties

• Basic rate-equation structure
• 18 Species formulated
• Vacancy, Interstitial, Di-Int., Single He,
  He-Vac, Di-He, Bubbles (Nuclei, Matrix, GB, PPT)
  Avg. He in a Bubble, Avg. Bubble Radius, He in
  GB, He in PPT bubble
• Main HEROS-Code Features
• Includes Radiation Damage
• Spatial-temporal dependent
• Coupled nucleation/growth
• Bubble kinetics

Electric Conductivity
Mechanical Property
Thermal Conductivity
Reaction
Reference
Reference
By Vol Diffusion
Drift
By Surf Diffusion
Un-irradiated
By Vol Diffusion
Coalescence
By Surf Diffusion
Irradiated
Surface Loss
In first 0.1?m
Reference
Reference
CONCLUSIONS
Bubble-loop Complexes
Grain-boundary bubble
HAPL Condition on SiC

• Helium implanted SiC retains damage after
  annealing. At high appm (gt200) he-palatelets
  form, which can break up into disk-bubbles or
  result in gas-filled nano-cracks
• HEROs code can model spatial and temporal
  microstructure evolution including He-filled
  bubbles Thus HEROS can model helium bubble
  evolution as a function of time and location.
• Recently observed platelet and disc-bubbles in
  He-implanted SiC requires development of new
  models.

SiC-Armor Temperature History
Ion Implantation Profile in SiC/shot
Nano-platelets
REFERENCES
Defect-free fiber
1 J. Chen, P. Jung and H. Trinkaus, PRL, v82,
p.2709 PRB, v61, p.12923 2 H. Huang, N.M.
Ghoniem, et al., Modell. Simul. Mater. Sci. Eng.
3, 615, 1995 3 T. Maruyama, M. Harayama, JNM
329333 (2004) 10221028 4 E. Oliviero, M.
Beaufort, and J. F. Barbot, JAP, v93, 2003,
p.231 5 A. Hasegawa et al. JNM 307311 (2002)
11521156
Depleted Zone
(R.Raffray, HAPL Nov, 2005)
(S. Sharafat, HAPL March, 2006)
High Average Power Laser Program Workshop, Oak
Ridge National Laboratory, March 21-22, 2006