McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 2-1 Electronics Principles & Applications Eighth Edition Chapter 2 Semiconductors

McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved.

2-1

ElectronicsElectronics

Principles & ApplicationsPrinciples & ApplicationsEighth EditionEighth Edition

Chapter 2Semiconductors(student version)

Charles A. Schuler

©2013


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• Conductors and Insulators• Semiconductors• N-type Semiconductors• P-type Semiconductors• Majority and Minority Carriers• Other Materials• Band Gaps

INTRODUCTION


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Dear Student:

This presentation is arranged in segments. Each segmentis preceded by a Concept Preview slide and is followed by aConcept Review slide. When you reach a Concept Reviewslide, you can return to the beginning of that segment byclicking on the Repeat Segment button. This will allow youto view that segment again, if you want to.


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Concept Preview• The nucleus of any atom is positively charged.• Negatively charged electrons orbit the nucleus.• The net charge on any atom is zero because the

protons and electrons are equal in number.• The valence orbit is the outermost orbit.• Copper has only one valence electron and is an

excellent conductor.• Materials with a full valence orbit act as

insulators.• Materials with 8 electrons in the valence orbit act

as insulators.


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NN

NN

The center of an atom is called the nucleus.Most atoms have neutrons which have no charge.A nucleus also has protonsand they have a positive charge.

Negative electronsorbit the nucleus.


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NN

NN

This is a copper atom.

It has 29 protons.

It has 29 electrons.

Its net charge = 0.

Valence electron


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The valence electron is the important feature.

NN

NN

Valence electron

Its attraction to the nucleus is relatively weak.


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The valence electron

The nucleus plus the inner electron orbits

A simple model of the copper atom looks like this:


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Copper wire is usedto conduct electricitybecause the valence

electrons move freelythrough its structure.

Remember, the valenceelectrons are weakly

attracted to the nuclei.


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So far, we know that copper’s single valence electron makes it a good conductor. Other valence

arrangements are different.

Such a material acts as an electrical insulator.

The rule of eight states that a material as shown belowwould be stable since its valence orbit is full.

No VacancyThe valence is 8 and the orbit is full.


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Atomic quiz

The dense and central part of any atom iscalled the ________. nucleus

Atom net charge is 0 since the number of protonsequals the number of ______. electrons

The outermost orbit of all atoms is calledthe ________ orbit. valence

Good electrical conductors have freevalence ________. electrons

The magic number for valence stabilityis ________. eight


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Concept Review• The nucleus of any atom is positively charged.• Negatively charged electrons orbit the nucleus.• The net charge on any atom is zero because the

protons and electrons are equal in number.• The valence orbit is the outermost orbit.• Copper has only one valence electron and is an

excellent conductor.• Materials with a full valence orbit act as

insulators.• Materials with 8 electrons in the valence orbit act

as insulators.

Repeat Segment


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Concept Preview• Silicon has 4 valence electrons.• Silicon atoms can form covalent bonds with each

other.• Covalent silicon satisfies the rule of 8 and acts as

an insulator at room temperature.• Donor impurities have 5 valence electrons.• N-type silicon has been doped with a donor

impurity to make it semiconduct.• Acceptor impurities have 3 valence electrons.• P-type silicon has been doped with an acceptor

impurity to make it semiconduct.


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Atoms of the same type can join together and form covalent bonds.

This is an electron sharing process.

Silicon atoms have four valence electrons.


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The covalent sharing satisfies the rule of eight.

In this structure, one bond is formed with each neighbor.


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This is a silicon crystal.

It does not conduct because its valence electrons are captured by covalent bonds.


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Thermal carriers

Covalent bonds can be broken by heating a silicon crystal.

Free electron

Hole


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The thermal carriers support the flow of current.


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Heating silicon crystals to make them conduct is not practical!


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This is an arsenic atom.

A silicon crystal can be doped with a donor impurity.

1

2 3

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Each donor atom that enters the crystal adds a free electron.

Free electron


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Silicon that has been doped with arsenic is called N-type.

The free electrons in N-type silicon support the flow of current.


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This is a boron atom.

A silicon crystal can be doped with an acceptor impurity.

1

2 3Each acceptor atom that enters the crystal creates a hole.

Hole


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Silicon that has been doped with boron is called P-type.

The holes in P-type silicon support the flow of current.


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What are two practical methodsof making silicon semi conduct?

HoleFree electron

Add a pentavalentimpurity.

Add a trivalentimpurity.

(N-type) (P-type)


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This is an N-type crystal.

Due to heat, it could have a few free holes.

These are called minority carriers.


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This is a P-type crystal.

Due to heat, it could have a few free electrons.

These are called minority carriers.


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Semiconductor quiz

A pure silicon crystal, at room temperature,acts as an electrical ________. insulator

The current carriers, in N-type silicon, arecalled ________. electrons

The current carriers, in P-type silicon, arecalled ________. holes

The minority carriers, in N-type silicon, arecalled ________. holes

The minority carriers, in P-type silicon, arecalled ________. electrons


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Concept Review• Silicon has 4 valence electrons.• Silicon atoms can form covalent bonds with each

other.• Covalent silicon satisfies the rule of 8 and acts as

an insulator at room temperature.• Donor impurities have 5 valence electrons.• N-type silicon has been doped with a donor

impurity to make it semiconduct.• Acceptor impurities have 3 valence electrons.• P-type silicon has been doped with an acceptor

impurity to make it semiconduct.

Repeat Segment


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Silicon is the workhorse of the semiconductor industrybut compound semiconductors help out in key areas.

• Gallium arsenide• Indium phosphide• Mercury cadmium telluride• Silicon carbide• Cadmium sulfide• Cadmium telluride

Other Materials

Some researchers are investigating carbon nanotubes and graphene for possible future applications in electronics.


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This Kodak display uses organic light-emitting diodes.


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The energy band diagrams below show a gap between the conduction band and the valence band, but not for the

conductor. In doped silicon, the dopant band effectively narrows the gap and makes it easier for electrons to enter the

conduction band and support the flow of current.

No gap (in fact, the valence and conduction bands overlap.


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REVIEW

• Conductors and Insulators• Semiconductors• N-type Semiconductors• P-type Semiconductors• Majority and Minority Carriers• Other Materials• Band Gaps

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McGraw-Hill © 2013 The McGraw-Hill Companies, Inc. All rights reserved. 2-1 Electronics Principles & Applications Eighth Edition Chapter 2 Semiconductors