Palladium Related Defects in Silicon

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Palladium Related Defects in Silicon Rakesh
Dogra Punjab Technical University, INDIA A.P.
Byrne, D.A. Brett, M.C. Ridgway Australian
National University, AUSTRALIA
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• Motivation
• Fast Diffusion of Pd in Si
• Introduces Deep Levels in band gap
• Deep levels act as trap/recombination centres
• DLTS Pd has amphoteric behavior
• Acceptor in n-type Si
• Donor in p-type Si
• Large probability to form Pd-Dopant (P, As, Sb,
  B) pairs
• Pd can be gettered

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Motivation
Local Structure of isolated Pd and Pd related
defects (Pd-dopant, Pd-V, Pd-I pairs) can be
studied with Nuclear Hyperfine Methods
Perturbed Angular Correlation Spectroscopy
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Experimental Details

• Sample Preparation
• Cz-Si (100) were implanted with Phosphorus and
  Boron
• Doses 5e15 to 1e20 ions cm-3
• Samples annealed at 900oC for 10s using RTA

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Experimental Details

• PAC Probe
• 92Zr(12C,4ng)100Pd ?100Rh E 70 MeV
• Recoil energy 8 MeV
• Implantation Depth 3 mm deep into Si wafers
• Isochronal annealing in N2 atmosphere

Zr foil 2.5mm
12C Beam
Si wafer
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Experimental Details

• PAC Measurements
• Slow-Fast coincident using four conical BaF2
  scintillator detectors
• Perturbation spectra formed from coincidence
  counts
• Least squares fitted with
• Site 1 Damaged
• Site 2 Unperturbed
• Site 2 Defect specific
• From coupling constant nQ, the largest component
  of electric field gradient, Vzz is extracted

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Results
Well defined interaction frequency
5e17 P cm-3
1e18 P cm-3
2e18 P cm-3
5e18 P cm-3
1e19 P cm-3
1e20 P cm-3
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Results
P-Si
Thermally unstable
EFG Parameters
n-Si ? nQ 13.1(2) MHz ? h 0 ? Symmetric EFG ?
EFG orientation lt111gt
p-Si ? nQ 35.5(3) MHz ? h 0 ? Symmetric EFG ?
EFG orientation lt111gt
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Discussions
Similar EFG parameters in highly doped
n-Si -Same defect formation -Ruled out the
formation of Pd-dopant pairs -Defect pair
dissociate above TA 500oC -Maximum probe
fraction b/w TA 200-300oC -n-Si comprises
of excess vacancies (negative) -Formation of
PdSi-VSi pair, PRB 72 (2005) 193202 -Phosphorus
Diffusion Gettering of Pd !
EC
EF for n-Si
V-
Ei
EvEc-0.12(2)
EV
Unique interaction frequency for P dose 5e17
ions cm-3
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Discussions

• Strong EFG in highly doped p-Si
• Defect pair is observed between TA 550-750oC
• Around this temperature Pd diffuses
  interstitially
• Axially symmetric EFG
• Tentatively Pdi-BSi pair ? supported by
  theoretical calculations

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Discussions
Temperature dependence of EFGs Both pairs show
T3/2 dependence

• Different charge states of the defect complexes
• Effect is stronger for Pd-B pair

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• Acknowledgements
• Organizers for waiving off the registration fee
• Dept of Science Technology, India for
  financial support