fundamentals of semiconductor
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7/30/2019 Fundamentals of Semiconductor
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Semiconductor Fundamentals
OUTLINE
General material properties
Crystal structure
Crystallographic notation
Read: Chapter 1
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7/30/2019 Fundamentals of Semiconductor
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Spring 2007 EE130 Lecture 1, Slide 2
What is a Semiconductor?
Low resistivity => conductor High resistivity => insulator
Intermediate resistivity => semiconductor
conductivity lies between that of conductors and
insulators
generally crystalline in structure for IC devices
In recent years, however, non-crystalline semiconductors
have become commercially very important
polycrystalline amorphous crystalline
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7/30/2019 Fundamentals of Semiconductor
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Spring 2007 EE130 Lecture 1, Slide 4
From Hydrogen to Silicon
1
1s 2s 2p 3s 3p 3d
1 H 1 1s1
2 He 2 1s2
3 Li 2 1 1s2 2s1
4 Be 2 2 1s2 2s2
5 B 2 2 1 1s2
2s2
2p1
6 C 2 2 2 1s2
2s2
2p2
7 N 2 2 3 1s2 2s2 2p3
8 O 2 2 4 1s2 2s2 2p4
9 F 2 2 5 1s2 2s2 2p5
10 Ne 2 2 6 1s2 2s2 2p6
11 Na 2 2 6 1 1s2 2s2 2p6 3s1
12 Mg 2 2 6 2 1s2 2s2 2p6 3s2
13 Al 2 2 6 2 1 1s2 2s2 2p6 3s2 3p1
14 Si 2 2 6 2 2 1s2 2s2 2p6 3s2 3p2
15 P 2 2 6 2 3 1s2 2s2 2p6 3s2 3p3
16 S 2 2 6 2 4 1s2 2s2 2p6 3s2 3p4
17 Cl 2 2 6 2 5 1s2 2s2 2p6 3s2 3p5
18 Ar 2 2 6 2 6 1s2 2s2 2p6 3s2 3p6
Z Name Notation
2 3
# of Electrons
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Spring 2007 EE130 Lecture 1, Slide 5
The Silicon Atom
14 electrons occupying the 1st 3 energy levels: 1s, 2s, 2p orbitals filled by 10 electrons
3s, 3p orbitals filled by 4 electrons
To minimize the overall energy, the 3s and 3porbitals hybridize to form 4 tetrahedral 3sp orbitals
Each has one electron and
is capable of forming a bond
with a neighboring atom
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Spring 2007 EE130 Lecture 1, Slide 6
diamond cubic lattice
The Si Crystal
Each Si atom has 4nearest neighbors
lattice constant
= 5.431
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7/30/2019 Fundamentals of Semiconductor
7/12Spring 2007 EE130 Lecture 1, Slide 7
How Many Silicon Atoms per cm-3?
Number of atoms in a unit cell: 4 atoms completely inside cell
Each of the 8 atoms on corners are shared among cells
count as 1 atom inside cell
Each of the 6 atoms on the faces are shared among 2cells count as 3 atoms inside cell
Total number inside the cell = 4 + 1 + 3 = 8
Cell volume:
(.543 nm)3 = 1.6 x 10-22 cm3
Density of silicon atoms
= (8 atoms) / (cell volume) = 5 x 1022 atoms/cm3
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7/30/2019 Fundamentals of Semiconductor
8/12Spring 2007 EE130 Lecture 1, Slide 8
Compound Semiconductors
Ga
As
zincblende structure
III-V compound semiconductors: GaAs, GaP, GaN, etc.
important for optoelectronics and high-speed ICs
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7/30/2019 Fundamentals of Semiconductor
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Crystallographic Notation
Notation Interpretation( h k l) crystal plane
{ h k l} equivalent planes
[h k l
] crystal direction< h k l> equivalent directions
h: inverse x-intercept of plane
k: inverse y-intercept of plane
l: inverse z-intercept of plane(Intercept values are in multiples of the lattice constant;
h, kand lare reduced to 3 integers having the same ratio.)
Miller Indices:
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7/30/2019 Fundamentals of Semiconductor
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Crystallographic Planes and Si Wafers
Silicon wafers are usually cut
along a {100} plane with a flator notch to orient the wafer
during IC fabrication:
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11/12Spring 2007 EE130 Lecture 1, Slide 11
Unit cell:
View in direction
Crystallographic Planes in Si
View in direction
View in direction
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7/30/2019 Fundamentals of Semiconductor
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Summary
Crystalline Si: 4 valence electrons per atom
diamond lattice
each atom has 4 nearest neighbors 5 x 1022 atoms/cm3
Crystallographic notation
Miller indices are used to designate planes
and directions within a crystalline lattice
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