BiasInduced Doping Engineering

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Bias-Induced Doping Engineering
SungKyunKwan University Woo Jong Yu
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SWCNT Field Effect Transistor
Silicon FET
SWCNT FET
Nature, 393, 49 (1998), Tans S. J. et al. 1ST
fabricate of SWCNT-FET

• P-type SWCNT FET
• Complementary MOS technology need both of p and
  n type
• Si FET covalent bond with impurities
• - Boron (p-type) , Phosphorus (n-type)
• This method is not available to CNT FET

Nano Lett., 3, 783 (2003), Cui X. et al. Oxigen
effect near the contact
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Previous researches of doping
Adv. Mat., 17, 2430 (2005), Takenobu. T. P-type
doping with F4TCNQ
J. Am. Chem. Soc., 123, 11512 (2001), Shim M. et
al. N-type doping with polymer (PEI)
Science 290, 1552 (2000), Zhou C. et al. N-type
doping with alkali metal (K)
Nano Lett., 7, 3603 (2007), Peng. L. Low work
function metal (Sc) and nanotube Schottky
contacted induced n-type FET

• Chemical doping metal work function
• Hard to control of dopants position
• Unstable in ambient condition

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Nitronium hexafluoroantimonate
Science, 301, 1519 (2003), Strano M. S. et al.
J. Am. Chem.. Soc., 127, 5196 (2005), An K. et al.

• Nitronium hexafluoroantimonate (NHFA)
• NO2 ions make a bond with p-electron in the
  nanotubes p-type dopant
• Doped near the Fermi level
• Selective remove of metallic carbon nanotubes

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Self-assembled SWCNT TFT

• Self assembled SWCNT TFT from SNU Hongs group
• Length 4 um, width 3um
• HiPCO CNTs

Nat. Nanotech., 1, 66 (2006), Lee. M.
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Bias-Induced Doping with Ionic Adsorbates
a

• nitrohexafluoroantimony (NHFA) NO2 SbF6-
• Dissolved in methanol
• (a) Gate bias induced ionic dopant type control
• (b,c) S/D bias induced dopant position control
  (Schottky diode control)
• Removing the metallic CNT by Selective NO2 ion
  doping

b
c
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Gate Bias-Induced Doping Engineering
Positive gate bias
Negative gate bias
NO2
SbF6-
SbF6-
NO2
SbF6-
SbF6-
NO2
SbF6-
NO2
NO2
SbF6-
NO2
S
D
S
D


-
-

-
-



-
-
VDS 0.5 V, 1 mM
VDS 0.5 V, 1 mM
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S/D Bias-Induced Schottky Diode Engineering
Positive drain bias
Negative drain bias
-

-

NO2
NO2
NO2
NO2
NO2
NO2
S
D
S
D
-
-
-
-
-
-







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Schottky Barrier Engineering
J. Phys. Chem. A, 106, 6851 (2002), Sierraalta.
A. - Interaction between CNT-NO2
Nanotech., 18, 415202 (2007), Nosho. Y. - Dipole
direction CNT Source to - Decrease of Schottky
barrier
Nanotech, 18, 415202 (2007), Nosho.
Y. Metal-molecule bonding mechanism

• Dipole direction Au to CNT
• Increase of Schottky barrier

Current Applied Physics, 6S1, e99 (2006), An.
K. - Interaction between Au-NO2
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SEM images
(a) Before doping - Dopants are not
found (b) Gate bias induced doping -
Dopants are uniformly sprayed on channel (c)
Gate S/D bias induced doping - Dopants are
accumulated on a negatively charged source region
a
c
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Stability of Schottky diodes
After 3rd doping
After 70 oC, 12 h
After 2 months
c
a
b

• (a) After the 3rd droplets
• (b) Heated at 70?in ambient condition for 12
  hours
• (c) After two months in ambient condition

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Nitronium hexafluoroantimonate
Science, 301, 1519 (2003), Strano M. S. et al.
J. Am. Chem.. Soc., 127, 5196 (2005), An K. et al.

• NO2 ions make a bond with p-electron in the
  nanotubes p-type dopant
• Doped near the Fermi level
• Selective remove of metallic carbon nanotubes
• Selective doping of metallic CNTs and removing
• - Dispersion after NHFA treatment is not
  good

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Gate Bias-Induced removing of Metallic CNTs
Reducing of metallic CNTs by NO2 ion doping
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Conclutions

• P, n type doping control by gate bias
• Other ionic adsorbates can be chosen such that
  the adsorption of anions and cations can maximize
  the doping effect of n and p types in the CNT-TFT
• Doping position and Schottky diode direction
  control by drain bias
• Chemical bonding Induce strong bonding and long
  term stable doping
• Remove the metallic carbon nanotubes by selective
  NO2 ions doping

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Acknowledgement
Advisor
Analasys and measurement
SEM
RAMAN
Y. H. Lee
D. J. Bae
S. Y. Jeong
K. K. Kim
B. R. Kang
H. K. Park
S. J. Kim

• M. B. Lee, S. H. Hong (SNU) FET prepare

• S. P. Gaunkar, D. Pribat (Ecole polytechnique)
  measurement