An Introduction toAn Introduction toSemiconductor DevicesSemiconductor Devices

Donald Neamen

Images and illustrations from supplements of “An Introduction to Semiconductor

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Images and illustrations from supplements of An Introduction to Semiconductor Devices” , 4th Ed., Mc Graw Hill were used for this lecture materials.

Semiconductor MaterialsSemiconductor Materials

Elemental SC - Group 4 elements : C, Si, Ge

Alloysp , ,

- Sn, Pb?

Compound SC

- Binary : Si-Ge

- Ternary : (Al,Ga)As, (Al,In)As, (Cd,Mn)Te,Ga(As,P), (Ga,In)As, (Ga,In)P, (Hg,Cd)TeCompound SC

- Intermetallic compound - IV-IV(Si-Ge, Si-C) - III-V(Al-P,As,Sb; Ga-N,P,As,Sb; In-N,P,As,Sb), BN

(Ga,In)As, (Ga,In)P, (Hg,Cd)Te- Quaternary : (Al,Ga)(As,Sb), (Ga,In)(As,P)

III V(Al P,As,Sb; Ga N,P,As,Sb; In N,P,As,Sb), BN- II-VI(Zn-S,Se,Te; Cd-S,Se,Te; Hg-Se,Te), MgO

I II III IV V VI VII VIII

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

Ca/Zn

H Ti Pb Bi

a g S S C

K Ga Ge As Se Br Kr

Cd In Sn Sb Te

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Hg Ti Pb Bi

Semiconductor HistorySemiconductor Historyyy

1833; Fist semiconducting property of Ag2S by Faraday1833; Fist semiconducting property of Ag2S by Faraday1873; Discovery of photoconductivity of Se by Smith 1874; Observation of rectification by Braun 1879 Di f H ll ff t ( l t t t di d)1879; Discovery of Hall effect (electron not yet discovered)1911; The term “semiconductor” introduced by Konigsberg & Weiss1927; copper oxide rectifier by Grondahl & Geiger1931; photocell by Bergmann1939; Development of microwave (Si)1940s; IR detectors of sulphide, selenide, telluride; p , ,1949; Discovery of transistor action by Bardeen & Brattain 1950; Invention of transistor by Shockley, First amorphous semiconductor (α-Se) ~ present;~ present;IC (electronic industry), solid state laser, organic semiconductors, artificial compound semiconductors

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Physical Constants and unitsPhysical Constants and unitsyy

Avogadro's number: NA .6.02 10 23

Boltzmann's constant k ..1.38 10 23 jouleK

Electronic charge (magnitude): e ..1.60 10 19 ( )coul

Free electron rest mass me ..9.1094 10 31 ( )kg

Permeability of free space: μ0 ..( ).4 π 10 7 henrymm

Permittivity of free space ε0 ..8.854 10 14 faradcm

Planck's constant: h ..6.625 10 34 ( ).joule sec

Proton rest mass mp ..1.67 10 27 ( )kg

Speed of light in vacuum: c ..2.998 10 10 cmsecsec

eV ..1.60 10 19 joule (electron-volt) meV .10 3 eV

μsec 10 6 sec nA 10 9 amp pA 10 12 amp V volt

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μsec .10 sec nA .10 amp pA .10 amp V volt

μm .10 6 m nm .10 9 m Angstrom .10 10 m Å .10 10 m

Types of SolidsTypes of Solidsypyp

Amorphous materials (for instance, glass and rubber) have order within a few atomic or molecular dimensionsfew atomic or molecular dimensions .

Polycrystalline materials have a high degree of order over many atomic or molecular dimensions These orderedmolecular dimensions. These ordered regions, or single-crystal regions , vary in size and orientation with respect to one another. The single-crystal regions are called grains and are separated from one another by grain boundaries.Single-crystal materials ( for example, silicon, copper, and table salt) have a very high degree of order, or regular geometric periodicity, throughout their entire volume. The advantage of a gsingle-crystal material is that, in general, its electrical properties are superior to those of a nonsingle-crystal material, since grain boundaries tend to degrade

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since grain boundaries tend to degrade the electrical characteristics.

SiOSiO22/Si/Si22

HRXTEM view of Si/SiO2

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Defects in MaterialDefects in Material

Point defect (0-D) Surface defect (2-D)Grain boundary

Vacancy

Interstitial

Grain boundary

ex) ImpuritiesSubstitutional

Interstitialimpurity

Substitutionalimpurity Bulk defect (3-D)

Precipitate

Line defect (1-D)

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Edgedislocationline

Point DefectsPoint Defects

A vacancy in the crystal. A substitutional impurity in the crystal. Theimpurity atom is larger than the host atom.

A substitutional impurity inthe crystal. The impurity atomis smaller than the host atom

An interstitial impurity in the crystal. Itoccupies an empty space between host atoms.

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is smaller than the host atom.

Line DefectsLine Defects

AC

A screw dislocation in a crystal.

D

Dislocation line

CompressionTension

A BDislocation

y

A BDislocationlineA edge dislocation in a crystal is a line defect

which is accompanied by lattice distortion and hence a lattice strain around it.

D C

Atoms in theupper portion.

Atoms in thelower portion .

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The screw dislocation in as viewed from above.

Line DefectsLine Defects

InGaAs/AlGaAs QWs

dislocations

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Surface DefectsSurface Defects

CrystalliteNuclei y

Liquid

Self interstitial typeatomForeign impurity

(b)

Liquid

( )

Strainedbond

Grainboundary

Void, vacancySelf-interstitial typeatom(b)(a)

Brokenbond(danglingbond)

GrainboundaryGrainGrainboundary

(c)Solidification of a polycrystalline solid from the melt. (a) Nucleation. (b) Growth (c) The solidified polycrystalline solid For simplicity cubes

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Growth. (c) The solidified polycrystalline solid. For simplicity, cubes represent atoms.

Primitive and Unit cellsPrimitive and Unit cells

LatticeUnit cell

: Periodic arrangement of atoms in the crystal→ Dots can be used for representing the atomic arrays: Lattice

Primitive unit cell

3-D unit cell

Primitive unit cell

Two dimensional lattice

- Unit cell : A small of the crystal that can be used to reproduce the entire crystal r = p a + q b + s c (p, q, s = integers)

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Basic Crystal StructuresBasic Crystal Structuresyy

Cubic Lattices

Simple Cubic (SC) Body-Centered Cubic (BCC) Face-Centered Cubic (FCC)

(000) (000)1 1 12 2 2

⎛ ⎞⎜ ⎟⎝ ⎠

(000) 1 1 02 2

⎛ ⎞⎜ ⎟⎝ ⎠

1 102 2

⎛ ⎞⎜ ⎟⎝ ⎠

1 102 2

⎛ ⎞⎜ ⎟⎝ ⎠

Q1: How many atoms are included in each unit cell ?Q2: What are the packing densities ?

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Miller indexMiller index

cUnitCell Geometry

zz

Unit cellLattice direction

cy

c

bOα

βc

yyxo

Pzo [121]

xba

aγ

A parallelepiped is chosen to describe geometry of ait ll W li th d ith th d f

abx

yyoo

Identification of a direction in a crystal

[001] [111]

unit cell. We line the x, y and z axes with the edges ofthe parallelepiped taking lower-left rear corner as theorigin

[010]

[100]

[010]

[110] [110]

-a-yax

y

[ ] [110] [ ][111]

[111]

[111][111]

Directions in cubic crystal system

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[111] [111]

[111]

[111] Family of <111>directions

Crystal plane and Miller indexCrystal plane and Miller indexy py p

Index of Plane

1 1 1 , , p q s

Plane⎛ ⎞

= ⎜ ⎟⎝ ⎠

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Crystal plane and Miller indexCrystal plane and Miller indexy py p

z(010) (010) (010)(010)

z

y

(010) (010)

(010)

y

Miller Indices (hk ):1 1

11 (210)1

2

z intercept at ∞ b

cx intercept at a/2

∞

(001) (110)xx

ax

y

x intercept at /2

y intercept at bUnitcell (100) z

Identification of a plane in a crystal (111)

y

(110)z

y

(111)

- z

x

x

- yy

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Various planes in cubic lattices

The Structure of Solids and Surfaces

Bulk termination : FCC

FCC (110)FCC (110)

FCC (100) FCC (111)

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The Structure of Solids and Surfaces

Bulk termination : BCC

BCC (110)BCC (110)

BCC (100) BCC (111)

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Crystal plane and Miller indexCrystal plane and Miller indexy py p

ex) Calculate the surface density of (110) plane in fcc. ao = 4.5 Å.

( ) 22 atoms 2 atomsSurface density = = Q1: Surface density of (111) plane in fcc

( )( ) ( )280 0

14 2

ya 2a 2 4.5 10

= 6.98 10 atoms/cm

−× ×

×

y ( ) p

Q2: ao = 4.75 Å. Calculate the surface densities

of (100) and (110) planes in bcc.

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Semiconductor StructureSemiconductor Structure

Diamond Cubic Structure

[ ]fcc fcc+ •14 111

Q1: How many atoms in unit cell ?Q2: Coordinates of atoms in unit cell ?Q ?

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Q3: What are the packing densities ?

Semiconductor StructureSemiconductor Structure

Diamond cubic structure has

- 8 atoms/unit cell- atomic packing factor = ~34 %- covalent bonding, tetragonal unit, 4 nearest neighborsg, g , g

a0

0 01/2

1/43/4

a0/2

3/41/4

1/21/2 0

[ ]1

00 1/2

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[ ]fcc fcc+ •14 111

Semiconductor StructureSemiconductor Structure

Zincblende structure Differs from the diamond structure only in that there are two types of atoms in the lattice

- GaAs crystal structurefcc 4 Ga atoms

[ ]14 111 fcc• 4 As atoms, or vice vera.[ ]4 f 4 As atoms, or vice vera.

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Semiconductor GrowthSemiconductor Growth

Purity & Doping

Purity : unintentionally doped (undesired) impurities- Purity : unintentionally doped (undesired) impuritiesSi : 1 per 109 Si atoms

- Dopants : intentionally added impuritiesPractical functioning of devicesPractical functioning of devices

Crystal Growth

Electronic grade poly Si- Electronic grade poly-Si

Silica Impureili SiCl4 Ultrapure

SiCl Poly-Sisilicon SiCl4 SiCl4 Poly Si

Reduction Chlorination Distilation H-Reduction

- Single crystal growingCzochralski method

Single crystal seed

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Crystal pulling and rotation

Semiconductor GrowthSemiconductor Growth

(Mitsubishi website at http://www.egg.or.jp/MSIL/english/index-e.html)

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Semiconductor GrowthSemiconductor Growth

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HomeworkHomework

Ch.1

4 (d), 7, 10, 14, 16, 19, 25

Due date:

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