Material Properties: I

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ECE-305: Spring 2016

Material Properties: I

Professor Mark Lundstrom Electrical and Computer Engineering

Purdue University, West Lafayette, IN USA lundstro@purdue.edu

1/12/15

Pierret, Semiconductor Device Fundamentals (SDF) pp. 3-11

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semiconductors

“One shouldn’t work on semiconductors, that is a filthy mess; who knows whether any semiconductors exist.” Wolfgang Pauli, 1931

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outline

1.  Silicon

2.  Crystals

semiconductors

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http://en.wikipedia.org/wiki/Periodic_table

column IV

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silicon energy levels

1S2

2S2

2P6

3S2

3P2

4S0

Si atom (At. no. 14)

4 valence electrons 8 valence states

“core levels”

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ener

gy

Si atoms in a solid

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1) In a Si crystal, each atom occupies, a specific location in a crystal lattice.

2) Polycrystalline Si consider of many

crystalline “grains” with different orientations. 3) In amorphous Si, the atoms are more or less

randomly distributed throughout the solid.

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a 2D crystal

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a

b

Graphene: 2011 Nobel Prize in Physics

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Graphene is a one-atom-thick planar carbon sheet with a honeycomb lattice.

source: CNTBands 2.0 on nanoHUB.org

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unit cells

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3D crystal structure

10 Lundstrom ECE-305 S16 http://en.wikipedia.org/wiki/Bravais_lattice

lattice plus basis

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semiconductors

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http://en.wikipedia.org/wiki/Periodic_table

column IV

semiconductors

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http://en.wikipedia.org/wiki/Periodic_table

Col. III

Col. V

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Si crystal structure (diamond lattice)

Natoms ≈ 5×1022 cm-3

5.43 A

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4 nearest neighbors

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diamond lattice

https://nanohub.org/tools/crystal_viewer

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The diamond lattice

https://nanohub.org/tools/crystal_viewer

Atoms per unit cell 8 times 1/8 + 6 times ½ + 4 8 atoms per unit cell

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Silicon: density

https://nanohub.org/tools/crystal_viewer

Lattice constant: a = 5.4307 Ang Density = total mass/vol. of unit cell. Atomic mass of Si: 28.0855 amu 1 amu = 1.6605 x 10−27 kg

ρ = 8× 28.0855×1.6605×10−27

5.4307 ×10−10( )3 kg/m3

ρ = 2.3296 g/cm3

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Silicon: NN spacing

https://nanohub.org/tools/crystal_viewer

Lattice constant: a = 5.4307 Ang Body diagonal = sqrt(3) a. NN spacing = sqrt(3)a/4

“cartoon” Si crystal

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outline

1.  Silicon

2.  Crystals

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https://nanohub.org/tools/crystal_viewer Online tool: