First principles simulations of nanoelectronic devices

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First principles simulations of nanoelectronic
devices
Jesse Maassen (Supervisor Prof. Hong
Guo) Department of Physics, McGill University,
Montreal, QC Canada
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Why first principles theory?
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Why first principles theory?
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How to calculate transport properties?
Taylor et al., PRB 63, 245407 (2001) Waldron et
al., PRL 97, 226802 (2006) Maassen et al., IEEE
(submitted)
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Applications.

• Graphene-metal interface
• Localized doping in Si nano-transistors
• Dephasing in nano-scale systems

Maassen et al., Appl. Phys. Lett. 97, 142105
(2010) Maassen et al., Nano. Lett. 11,151 (2011)
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Applications.

• Graphene-metal interface
• Localized doping in Si nano-transistors
• Dephasing in nano-scale systems

Maassen and Guo, preprint to be submitted
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Applications.

• Graphene-metal interface
• Localized doping in Si nano-transistors
• Dephasing in nano-scale systems

Maassen et al., PRB 80, 125423 (2009)
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Applications.

• Graphene-metal interface
• Localized doping in Si nano-transistors
• Dephasing in nano-scale systems

Maassen et al., PRB 80, 125423 (2009)
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Application Graphene-metal interface

• Motivation

• Graphene has interesting properties (i.e., 2D
  material, zero gap, linear dispersion bands, ).

• For electronics, all graphene sheets must be
  contacted via metal electrodes (source/drain).

• Theoretical studies exclude accurate treatment of
  electrodes.

• How does the graphene/metal interface affect the
  response of a device?

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Application Graphene-metal interface

• Transport properties

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Application Graphene-metal interface

• Atomic structure

• Cu, Ni and Co (111) have in-place lattice
  constants that almost match that of graphene.

• Equilibrium interface structure determined from
  atomic relaxations.

Maassen et al., Appl. Phys. Lett. 97, 142105
(2010) Maassen et al., Nano. Lett. 11,151 (2011)
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Application Graphene-metal interface

• Ni(111) contact

• Linear dispersion bands near Fermi level.
• Zero band gap.
• States only in the vicinity of K.

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Application Graphene-metal interface

• Ni(111) contact

• Strong hybridization with metal
• Band gap opening
• Graphene is spin-polarized

Maassen et al., Nano. Lett. 11, 151 (2011)
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Application Graphene-metal interface

• Ni(111) contact

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Application Graphene-metal interface

• Ni(111) contact

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Application Localized doping in Si
nano-transistors

• Motivation

• Leakage current accounts for 60 of energy in
  transistors.

• Two sources (i) gate tunneling and (ii)
  source/drain tunneling.

• How can highly controlled doping profiles affect
  leakage current ?

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Application Localized doping in Si
nano-transistors

• Structure n-p-n and p-n-p.
• Channel doping B or P.
• L 6.5 nm ? 15.2 nm
• Si band gap 1.11 eV

Technical details regarding random doping,
large-scale modeling and predicting accurate
semiconductor band gaps can be found in the
thesis.
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Application Localized doping in Si
nano-transistors

• GMAX / GMIN 50.

• Lowest G with doping in the middle of the channel.

Maassen and Guo, preprint to be submitted
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Application Localized doping in Si
nano-transistors
Maassen and Guo, preprint to be submitted
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Application Localized doping in Si
nano-transistors
Maassen and Guo, preprint to be submitted
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Application Localized doping in Si
nano-transistors

• G decreases with L.

• Variations in G increase dramatically with L.

Maassen and Guo, preprint to be submitted
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Application Localized doping in Si
nano-transistors

• G decreases with L.

• Variations in G increase dramatically with L.

Maassen and Guo, preprint to be submitted
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Summary

• First principles transport theory is a valuable
  tool for quantitative predictions of
  nanoelectronics, where atomic/quantum effects are
  important.

• I determined that the effect of metallic contacts
  (Cu, Ni, Co) can significantly influence device
  characteristics. I found that the atomic
  structure of the graphene/metal interface is
  crucial for a accurate treatment.

• My simulations on localized doping profiles
  demonstrated how leakage current can be
  substantially reduced in addition to alleviating
  device variations.

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Thank you!
Questions ?