AKMA BINTI CHE ISHAK

NOOR INDON BINTI ABDUL SAMAD

NOR HASRIMIN BINTI MD NOR
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A K M A B I N T I C H E I S H A K

N O O R I N D O N B I N T I A B D U L S A M A D

N O R H A S R I M I N B I N T I M D N O R
Authors
Authors Copyright © 2021

Electrical Engineering Department

Politeknik Tuanku Sultanah Bahiyah

09000 Kulim, Kedah

AKMA BINTI CHE ISHAK

SENIOR LECTURER

ELECTRICAL ENGINEERING DEPARTMENT

POLITEKNIK TUANKU SULTANAH BAHIYAH

NOOR INDON BINTI ABDUL SAMAD

SENIOR LECTURER

ELECTRICAL ENGINEERING DEPARTMENT

POLITEKNIK TUANKU SULTANAH BAHIYAH

NOR HASRIMIN BINTI MD NOR

SENIOR LECTURER

ELECTRICAL ENGINEERING DEPARTMENT

POLITEKNIK TUANKU SULTANAH BAHIYAH

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i | I N T R O D U C T I O N O F S E M I C O N D U C T O R
Authors
Authors

ACKNOWLEDGEMENT
ACKNOWLEDGEMENT

Alhamdulillah, praises to Allah SWT, with His grace and mercy, the eBook

Semiconductor Devices has finally completed. We would like to express

our appreciation to the e Learning Politeknik Tuanku Sultanah Bahiyah

which gave opportunities and inspiration to produce this eBook. Our

experience in the teaching and learning process of the previous

subject is an advantage that guides us along the way.

The editor would like to give highest regards and appreciation to all

who have been involved either directly or indirectly in making this

project eBook work. Any positive feedback from lecturers and

students are mostly welcomed and appreciated. It is hoped that this

eBook will be one of the tiny steps that we have made to start the long

journey of road to excellent.

ii | I N T R O D U C T I O N O F S E M I C O N D U C T O R
Authors
Authors
ABSTRACT
ABSTRACT

The world would be a very various place if without semiconductors like no

electronic hand calculators, cellphones, electronically controlled transmission or

personal computer. The eBook Semiconductor Devices is a comprehensive guide for

student and lecturers as references. Student can easily read the eBook even they

are not in a place that has internet coverage. It required memory in a device such as

a smartphone or laptop as storage space.

The biggest advantage of this eBook is the ability to own the book in a short period

of time. The content of this eBook Semiconductor Devices has been designed to

cater the Polytechnic’s syllabus requirement. It consists of notes, review question

and tutorial questions that can assist the students in the learning processes. This

eBook Semiconductor Devices will be useful to assist student in understanding

electronic device and circuits.

Key term: Semiconductor Devices, Polytechnic, eBook

iii | I N T R O D U C T I O N O F S E M I C O N D U C T O R
TABLE OF CONTENTS

DECLARATION ii
ACKNOWLEDGMENTS ii
ABSTRACT iii
LEARNING OUTCOMES iv

1.0 CHARACTERISTICS AND ELECTRICAL

PROPERTIES OF SEMICONDUCTORS 3-6

2.0 ATOMIC STRUCTURE 7-9

TUTORIAL QUESTION 10

3.0 COVALENT BONDS IN SEMICONDUCTORS 11-12

TUTORIAL QUESTION
13

4.0 CHARACTERISTICS AND ELECTRICAL

PROPERTIES OF SEMICONDUCTORS 14

4.1 INTRINSIC AND EXTRINSIC SEMICONDUCTORS14

4.2 DIFFERENCE BETWEEN INTRINSIC

15
AND EXTRINSIC SEMICONDUCTOR

5.0 THE DOPING PROCESS 16

5.1 P-TYPE SEMICONDUCTOR 17-18

5.2 N- TYPE SEMICONDUCTOR 19-20

TUTORIAL QUESTION 22

6.0 FORMATION OF PN JUNCTIONS 23

6.1 FREE ELECTRONS MOBILITY 23-24

6.2 FORMATION OF A DEPLETION REGION 25-26

TABLE OF CONTENTS

7.0 PN JUNCTION REACTIONS TOWARDS

VOLTAGE BIASING
27

7.1 BIAS 28

7.2 FORWARD BIAS 29 -30

7.3 REVERSED BIAS 31 -32

7.3 LEAKAGE CURRENT 33

TUTORIAL QUESTION 34

SUMMARY 35

NOTES 36

TUTORIAL QUESTION

MULTIPLE CHOICE QUESTIONS 37-38

SHORT ANSWER QUESTIONS 39

TRUE/FALSE QUESTIONS 40

ESSAY QUESTIONS 41

TUTORIAL ANSWER

TUTORIAL PAGE 10 37-38

TUTORIAL PAGE 13 39

TUTORIAL PAGE 22 40

MULTIPLE CHOICE 45

SHORT ANSWER QUESTIONS 46

TRUE/FALSE QUESTIONS 47

ESSAY QUESTIONS 48-50

REFERENCES 51
 INTRODUCTION
INTRODUCTION

TO
TO

SEMICONDUCTORS
SEMICONDUCTORS

LEARNING OUTCOMES

At the end of this chapter, you should be able to:

Describe semiconductor of silicon and germanium

Describe the characteristics of n-type and p-

type semiconductors

Explain the formation of p-n junction

Explain meaning of forward biased voltage and

reverse biased voltage supplied across a P-N

junction.

Discuss effects when a P-N junction is supplied

with forward biased voltage and reverse biased

voltage

iv | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 INTRODUCTION

Atoms are the main core of all materials. It is the smallest units that

make up a substance. Atomic structure can be used to determine

the electrical properties of substance.

Electronic component and device are made of semiconductor as

electrical materials. To understand more about the use of

semiconductors, the importance things to know is the

characteristic and electrical properties of it. In this chapter, it will be

more focused on the atomic structure of semiconductor

materials, the p-n junction reactive towards voltage biasing and

their properties.

As you know, there is prescribed energy band, that the electrons

of an atom can exist within it. Each shell around the nucleus

corresponds to a certain energy band and is separated from

adjacent shells by band gaps, in which no electrons can exist.

An insulator is functioned to not allow the electrical current flow

through it. The material itself does not conduct electrical current

when working in normal condition.

For the high-performance insulators, it is compounds rather than

single-element materials and it also will have a very higher

resistivities.

0 1 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
NICE TO KNOW

Conductors have many

free electrons whereas

insulators have very

few or none at all.

The valence atom in the material have a tight bound to the atoms and will

result a very few free electrons that can flow across the insulator. For

example, such as rubber, plastics, glass, mica, and quartz.

A conductor is functioned to allow current flow through it. The materials itself

is good conductor such as metal. The best conductors are single-element

materials, such as copper (Cu), silver (Ag), gold (Au), and aluminum (Al), which

are characterized by atoms with only one valence electron very loosely

bound to the atom. The free electron inside conductor is the loosely bound
SILICON

valence electrons. This may result in a conductive material the free electrons

are valence electrons.

A semiconductor is a material that can conduct electrical current through it.

The condition of the materials is between conductors and insulators. A

semiconductor in its pure (intrinsic) state is neither a good conductor nor a

good insulator.

A commonly used of single-element semiconductor such as antimony (Sb),

GERMANIUM
arsenic (As), astatine (At), boron (B), polonium (Po), tellurium (Te), silicon (Si), and

germanium (Ge). For compound semiconductors that usually being used such

as gallium arsenide, indium phosphide, gallium nitride, silicon carbide, and silicon

germanium. The characteristic of the single-element semiconductors is the

atom with for valence electrons. The most commonly semiconductor that

being used use in the industry nowadays is Silicon.

0 2 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 1.0 CHARACTERISTICS AND ELECTRICAL

PROPERTIES OF SEMICONDUCTORS

The materials can be divided into conductors, insulators and semiconductors by determine their

electrical conductivity. The material that allows current to flow through it easily are called

conductor.

The reason because valence electron can easily become free electron that can flow throughout

the material due to its atoms that have valence electrons that is not strong enough to be held by

nucleus. However, for the insulator materials, its valence electrons are tightly bound and because

of this, it does not conduct electricity.

A material with electrical conductivity that lies between those of insulators and conductors are

called semiconductor. Semiconductor materials can conduct electricity better than insulators but

not as good as conductors. The semiconductor atoms have four valence electrons. The total of

free electron numbers is not fix depend on external condition such as increasing and decreasing

temperature of the materials or by adding the voltage to the semiconductors. The best and

commonly use semiconductors is silicon.

0 3 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Insulators have tightly bound

electrons in their outer shell.

These electrons require a

very large amount of energy

to free them for conduction.

The force on each electron is

not enough to free it from its

orbit and the insulator does

not conduct. Insulators are

said to have a high resistivity

or resistance.

Figure 1 . 1 : Insulator

Conductors have loosely bound

electrons in their outer shell. These

electrons require a small amount of

energy to free them for conduction.

The force on each electron is enough

to free it from its orbit and it can

Figure 1. 2 : Conductor

jump from atom to atom.

Conductors are said to have a low

resistivity or resistance.

0 4 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 The total atomic number of silicon is 14. This means that inside its nucleus it has 12 protons

that balanced by 14 orbiting electrons. The very outermost of the ring of an atom is called

the valence ring and the electrons in this ring are called valence electrons. There are four

valence electrons for all semiconductors. In order to determines its electrical conductivity,

it depend on number of valence electron possessed by any atom.

In order to determines how it will combine with other atoms it depends on the

number of valence electron also. In order to determine whether the conductor is the

best or not, by checking the number of valence electron. If there is only one valence

electron that’s means it is the best conductor. It also to determine whether the

insulator is the best or not, by checking the number of valence electron. If there are

complete shells, that’s means it is the best insulator. The characteristics of

conductors, insulators and semiconductors are summarized in Table 1.

0 5 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Table 1 : Characteristics of conductors, insulators and semiconductors

CHARACTERISTICS CONDUCTOR INSULATOR SEMICONDUCTOR

Conducts electricity Does not conduct Electrical conductivity

Conductivity

electricity intermediate between

insulator and conductor

Valence electrons 1-3 valence electrons 5-8 valence electrons 4 valence electrons

Low resistivity. High resistivity. Atoms Does not easily release or

Resistivity

Atoms tend to release tend accept electrons accept electrons

valence electrons

Valence and Valence and conduction

Valence and conduction Valence and conduction band

conduction bands are separated by

bands are overlapped are separated by forbidden

forbidden energy gap of

energy gap of 1.1 eV

6 to 10eV

Temperature It has positive It has negative It has negative temperature

temperature temperature coefficient

coefficient

It has no forbidden gap

Forbidden gap It has large forbidden It has small forbidden gap

gap

Zero Kelvin Acts like a

Acts like an insulator Acts like an insulator

superconductor
behavior

Examples: copper, Examples: glass, Examples: silicon,

Examples

silver, aluminum plastics, ceramics germanium, carbon

0 6 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 2.0 Atomic Structure

The atomic structure model was introduced by Niels Bohr in 1913. Atoms is built of

nucleus and electrons. The nucleus are combination of protons and neutrons. Positive

charged are called protons while negative charged are called electrons.

For the neutrons it is unchanged. An atom’s structure is consisting of a nucleus in the

center and electron will move around it layer by layer. For this layer it is called shells.

The first shell (n=1) is called K, the second shell L (n=2), followed by M, N, O, P, and Q.

The valence electron stays at the outermost of the shell. The valence electron is used

to determine the electrical properties of the materials.

Electron orbit

Proton at

Electron
the nucleus

Figure 2.1 : Bohr’s atomic model

0 7 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
The maximum number of

electrons in each shell is given

by the following formula:

2 x n

From the formula given, the maximum number of electrons for each shell are

as depicted in Table 2.

Maximum number of
N Shell

electrons

1 K 2

2 L 8

3 M 18

4 N 32

5 O 50

6 P 72

7 Q 98

Table 2 .1 : Maximum number of electrons for each shell

0 8 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
Figure 2.2 shown the sample of atomic structures of silicon and

germanium which is the silicon atom has 14 electrons and a germanium

atom has 32 electrons. The electrons that are in the outermost shell

of an atom called valence electrons. In other words, these are the

electrons that can be gained or lost during a chemical reaction.

Shell

Nucleus

Electron

Figure 2.2 : Atomic Structure of silicon and germanium

0 9 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
TUTORIAL QUESTION

(Answer at end of chapter)

Using the atomic number from the periodic table in Table 2.2 .show a silicon (Si) atom using

an electron configuration table and draw simple diagram to show the atomic structures.

Table 2.2 : Periodic Table

1 0 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 3.0 COVALENT BONDS IN SEMICONDUCTORS

Atoms will always try to fill the maximum number of

electrons for their valence bands. A semiconductor has

four valence electrons. I order to complete the maximum

number of electrons, an atom in semiconductor will take

or share valence electron from nearby atoms, to

forming a covalent bond.

A bond formed between two atoms are called covalent

bond. I happened between two atoms when they try to

share one or more pairs of valence electrons.

Semiconductor will behave like insulator at room

temperature, due to strong and stable covalent bonds

between their atoms.

1 1 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 There are some aspects that interrupt covalent bonds

such as heat, temperature, potential different and the

doping process.

The covalent bonds will break due to this factor and some

electrons are freed to become free electrons. A small

amount of current will flow because a small number of

free electrons are produced if small voltage is applied to

the semiconductors.

More valence electrons will be freed from their bonds to

become free electrons if the temperature keep increase.

The semiconductor will become as conductor if the voltage

is kept continues to be supply and the current will keep

increase.

Shared electrons of a covalent bond

Figure 3.1 : Covalent bonds between silicon atoms

1 2 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
TUTORIAL QUESTION

(Answer at end of chapter)

a) What is the basic difference between conductors and insulators?

b) How do semiconductors differ from conductors and insulators?

c) How many valence electrons does a conductor such as copper have?

d) How many valence electrons does a semiconductor have?

e) Name three of the best conductive materials.

1 3 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 4.0 CHARACTERISTICS AND ELECTRICAL PROPERTIES OF

SEMICONDUCTORS

4.1 INTRINSIC AND EXTRINSIC

SEMICONDUCTORS

A pure substance to which impurity has been added are called

intrinsic semiconductors. At room temperature, the current

conductivity capability is low. The most frequently used intrinsic

semiconductors in electronic applications were Germanium and

Silicon.

To produced extrinsic semiconductors, a small number of impurities

need to be added to intrinsic semiconductors. It used to increase

either the number of free electrons or 'holes' in the semiconductor

crystal. I also increase the current conductivity.

The impurities added to semiconductors have two category which is

trivalent and pentavalent. Trivalent impurities consist of three

valence electrons while pentavalent impurities consist of five valence

electrons. Doping is the process to adding impurities to the

semiconductors.

1 4 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 4.2 DIFFERENCE BETWEEN INTRINSIC AND

EXTRINSIC SEMICONDUCTOR

An intrinsic semiconductor is the one which is made of the extremely

pure semiconductor material. They have the equal number of holes

and electrons so do not conduct the current. Extrinsic

semiconductors are made out of intrinsic semiconductors by adding

some suitable impurity (P-Type or N-Type) in an extremely small

amount.

Table 4.1 : Difference between Intrinsic and Extrinsic Semiconductor

CHARACTERISTICS INTRINSIC SEMICONDUCTOR EXTRINSIC SEMICONDUCTOR

Pure semiconductor (with an impurity) is Such semiconductors are made by adding

Purity

considered to have an intrinsic nature. impurities to pure semiconductors.

Conductivity Low High

They are practically used in various

They are not practically used
Use

applications.

The energy gap is more than that in an

Energy gap
Energy gap is small.

intrinsic semiconductor.

Number of electrons and holes are

Electrons vs Holes In N-type, electrons are in majority

equal.
whereas in P-Type, holes are in majority.

For P-Type: Gallium, Aluminum, Boron.

Silicon, Germanium
Examples

For N-Type: Phosphorous, Antimony, Arsenic.

Group IV elements lie in this Group III and V elements (as an impurity) are

Elements table category. introduced in Group IV elements.

Conductivity increases as Conductivity mainly depends on the

Conductivity Vs

temperature rises. impurity added.

Temperature

1 5 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 5.0 THE DOPING PROCESS

To produce an extrinsic semiconductor, the doping process is

needed. The doping process is the process of adding impurities to

an intrinsic semiconductor.

It will increase the number of free electron or ‘holes’. To generate

a p-type semiconductor, a semiconductor will need to be doped

with trivalent impurity.

Indium, gallium, boron and aluminum were example of trivalent

impurities. While phosphorus, arsenic and antimony were example

of pentavalent impurities.

An intrinsic semiconductor will be like insulator rather than a

conductor when the surrounding temperature is at room

temperature which is approximately 25˚C.

The conductivity of an intrinsic semiconductor is lower than an

extrinsic semiconductor. The higher number of impurity atoms will

increase the level of conductivity that have been added while

doping process activity.

1 6 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 5.1 P-Type Semiconductors

By adding trivalent impurities to intrinsic semiconductors, it will be

produced p-type of semiconductors. It will create excess holes which

can accept electrons.

Any impurities which can produce p-type semiconductors are known

as acceptor impurities. Figure 5.1 shows an example of a p-type

semiconductor formed by adding indium to silicon.

The atom that has only three valence electrons is called trivalent atom.

There is some examples of material such as aluminum (Al), boron (B),

and gallium (Ga). Atom that doped with large number of trivalent

impurities such as silicon crystal, may results in many holes, or vacancies

in the covalent bond structure of the material. At the vacancy area,

one more valence electron is needed for each trivalent atom for the

crystal to gain the maximum stability of electric charge with eight

electrons.

1 7 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
Indium has 3 valence electrons while silicon has four

valence electrons. Referring to Figure 5.1, notice that

indium contributes all three of its valence electrons to

form three covalent bonds with three silicon atoms.

Due to Indium atom has no more valence electron left,

one of the valence electrons consist of four silicon atoms

does not form a covalence bond. A hole was created

due to missing electron that left an empty space which

has a positive electric charge.

Majority current carriers are holes that is p-type

semiconductors while free electrons are the minority

current carriers. Due to the predominance of holes, it

has positive charge compare to free electron. It is p-

type semiconductor material where p is stands for

‘positive’.

Hole

Trivalent

impurity atom

Figure 5.1 : Formation of p-type material

1 8 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 5.2 N-Type Semiconductors

By adding pentavalent impurities to intrinsic semiconductors, the n-

type semiconductor can be produced.

Donor impurities is impurities which can produce n-type

semiconductors because they able to donate free electron to the

semiconductor.

Arsenic has five valence electron and for silicon it has four valence

electrons. As shown in Figure 5.2, arsenic contributes four valence

electrons to form four covalent bonds with four silicon atoms. Due to

this, the arsenic atom leaves with one excess valence electron will not

bonding. It will become a free electron.

The free electron will be negative current carrier. In n-type

semiconductors, the majority of current carrier is free electrons.

While in minority of current carriers, it is holes.Due to the

predominance of free electrons, that are negative compared to holes,

the semiconductor is called an n-type semiconductor, where n stands

for 'negative’. Table 5.1 show comparison of p-type and n-type

semiconductors.

1 9 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
The atom that has five valence electrons is called pentavalent

atom. There is some examples of materials such as antimony (Sb),

arsenic (As), and phosphorous (P).

Large number of pentavalent impurity atom when doped with a

silicon crystal may results in produce more free electrons in the

material. At the location of each pentavalent atom, there will

have one electron there and it is not used in the covalent bond

structure. Bear in mind, that there will be only eight electron that

can be exist in the outer ring on every atom.

This may result one of the valent electrons is the pentavalent

impurity is not needed in the structure of the covalent bond and

will be free electron that will floating across the material.

free electron

Pentavalent

impurity atom

Figure 5..2 : Formation of n-type material

2 0 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Table 5.1 : Comparison between p-type and n-type semiconductors

PARAMETER P - TYPE SEMICONDUCTOR N- TYPE SEMICONDUCTOR

Nature of doping element Acceptor type

Donor type

Impurity added in doping

Pentavalent
Trivalent

process

Majority current carrier

Holes Electrons

Minority current carrier Electrons Holes

Conductivity Due to presence of holes Due to presence of electrons

Concentration of Low Very high as compares to p type

semiconductor
electrons

Comparatively less than p type

High
Concentration of holes
semiconductor

2 1 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
TUTORIAL QUESTION

(Answer at end of chapter)

a) What is the purpose of doping process?

b) What type of semiconductor material is created when a silicon crystal is doped with

pentavalent impurity atoms?

c) Identify how many electrons are presented at valence layer of the trivalence atoms for

doping process.

d) What are the minority current carriers in a p-type semiconductor material?

e) Does a hole exhibit a positive, negative, or neutral charge?

2 2 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 6.0 Formation of p-n Junctions

6.1 Free Electrons mobility

When there is no voltage or electric field applied across the semiconductor, the

free electrons moves randomly.

However, when the voltage or electric field is applied across the semiconductor,

each free electron starts to move more quickly in particular direction. Electrons

move very fast in vacuum.

According to conventional current theory, current flows from the positive

terminal to the negative terminal because current flows from a higher potential to

a lower potential.

2 3 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
The positive terminal has higher potential than the negative terminal. According to electron

current theory, electrons flow from the negatives terminal to the positive terminal.

Free electrons are electrons freed from covalent bonding. An electron is a current carrier

and since it is negatively charged it is called a negatives current carrier. When an electron

moves, it leaves a space called a hole.

Holes are considered to be positively charged. They attract electrons to fill the empty

spaces. The movement of electrons causes current flow in semiconductors.

Figure 6.1 : Electron and hole pair

2 4 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 6.2 Formation of a Depletion Region

When p-type and n-type materials are combined together, they form a p-n junction. p-

Type materials contain holes as majority carriers while n-type materials contain electrons as

majority carriers. When these two materials are combined, the free electrons in the n-type

material are pulled to replace the holes in the p-type material.

Diffusion of electrons occurs across the junction until it stops when the barrier voltage is

reached. The area around the p-n junction is called a depletion region and it is electrically

neutral.

The barrier voltage depends on the type of semiconductor, temperature, and doping

densities. The barrier voltage for silicon is 0.7 V and 0.3 V for germanium.

2 5 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 At the moment of p-n junction formation, the free electrons of the n-type semiconductor

begin to diffuse across the junction to combine with holes in the p-type semiconductor.

This process will create a layer of positive charge between the n-type semiconductor and the

junction since the n-type semiconductor loses its free electrons.

As the electrons and holes combine, a layer of negative charge will form between the p-type

semiconductor and the junction since the p-type semiconductor loses its holes. The positive and

negative layer near the junction form a depletion region as illustrated in Figure 6.2.

Depletion region

Positive charge layer

Negative charge layer

Figure 6.2 : Formation of p-n junction

2 6 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 7.0 PN Junction Reactions

towards Voltage-Biasing

Voltage supplied to a p-n junction is known as bias voltage. Blas voltage

will determine whether current can flow across the p-n junction or

not.

There are two types of bias voltage, namely forward bias and reverse

bias. Current can flow in a forward biased condition but cannot flow in

a reverse biased condition.

2 7 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 7.1 Bias

The term bias is defined as a control voltage or current. The term bias

refers to the application of DC voltage to set up certain operating

conditions. Or when an external source of energy is applied to a P-N

junction it is called a bias voltage or simply biasing.

This method either increases or decreases the barrier potential of

the junction. As a result, the reduction of the barrier potential causes

current carriers to return to the depletion region.

Following two bias conditions are applied in PN junctions:

Forward Biasing
An external voltage is added of the same polarity to the barrier potential,

which causes an increase in the width of the depletion region.

Reverse Biasing
A PN junction is biased in such a way that the application of external voltage

action prevents current carriers from entering the depletion region.

2 8 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 7.2 Forward Bias

Forward-biasing a diode allows current to flow easily through the

diode. Figure 7.1 illustrates a p - n junction that is forward-biased. In

Figure 7.1 , notice that the n material is connected to the negative

terminal of the voltage source, V and the p material is connected to

the positive terminal of the voltage source, V.

The voltage source, V must be large enough to overcome the internal

barrier potential VB. The voltage source repels free electrons in the n

side across the depletion zone and into the p side.

Once
on th
e p side
, the fr
ee electr
on falls in
will th to a ho
en travel le. The el
from ectron
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term trac ted to
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2 9 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Figure 7.2 shows the schematic symbol of a diode with the voltage

source, V connected to provide forward bias. Notice that forward bias

exists when the anode,

A is positive with respect to the cathode, K. Notice that electrons flow

to the n side, against the arrow on the diode symbol. The arrow on the

diode symbol points in the direction of conventional current flow.

Either current direction works well when analyzing diode circuits.

However, we will use electron flow when analyzing circuits containing

diodes.

Figure 7.1 : Depletion region when

supplied with forward bias

Figure 7.2 : Electron flow is against the

arrow,

3 0 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 7.3 Reverse Bias

The p- n Junction Figure 7.3 show how to reverse-bias a p - n junction. Notice

that the negative terminal of the voltage source, V, is connected to the p -type

semiconductor material and that the positive terminal of the voltage source, V, is

connected to the n -type semiconductor material.

The effect is that charge carriers in both sections are pulled away from the

junction. This increases the width of the depletion zone, as shown. Free electrons

on the n side are attracted away from the junction because of the attraction of

the positive terminal of the voltage source, V. Likewise, holes in the p side are

attracted away from the junction because of the attraction by the negative

terminal of the voltage source, V.

Figure 7.3 : Depletion region when supplied with reverse bias

3 1 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
In Figure 7.4 shows the schematic symbol of a diode with
the voltage source V , connected to provide reverse bias.

The result of reverse bias is that the diode is in a

nonconducting state and acts like an open switch, ideally
with infinite resistance.

Figure 7.4 : Schematic symbol

3 2 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
7.4 Leakage Current

Even a reverse-biased diode conducts a small amount of

current, called leakage current. The leakage current is mainly

due to the minority current carriers in both sections of the

diode.

The minority current carriers are holes in the n side and free

electrons in the p side. The minority current carriers exist as a

result of thermal energy producing a few electron-hole pairs.

Since temperature determines the number of electron-hole

pairs generated, leakage current is mainly affected by

temperature.

Any increase in the temperature of the diode increases the

leakage current in the diode. These minority current carriers

move in a direction that is opposite to the direction provided with

forward bias

3 3 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Re
mi
nd
er
s
Tu
to
ria
Qu l
es
tio
n

1
The p side of a diode is called the (anode/cathode) and

the n side is called the (anode/cathode).

2
To forward-bias a diode, the anode must be

(positive/negative) with respect to its cathode.

3 A reverse-biased diode acts like an (open/closed)

switch.

3 4 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 SUMMARY

RECAP 1

Materials can be classified as conductors, semiconductors and

insulators based on their electrical conductivity.

RECAP 2 RECAP 4

The properties of materials are A p n junction is formed when p-type and

determined by their atomic structure n-type materials are combined together

especially their valence electrons.

Semiconductors are materials with P-n junctions are more useful when bias

electrical conductivity between those of voltage is applied.

conductors and insulators.

RECAP 3 RECAP 5

Silicon and germanium are commonly used There are two types of bias voltage,

semiconductors. namely forward bias and reverse bias.

P-Type or N-type material can be

Now that we understand the basic

produced by adding impurities to pure

characteristics of semiconductors and the

semiconductors through the doping

effect of voltage biasing on p n junctions,

process.

3 5 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 s
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3 6 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 TUTORIAL QUESTIONS
Multiple-Choice Questions

1. The most widely used semiconductive material in electronic devices is

A. germanium

B. carbon

C. copper

D. silicon

2. Select the statement which explains the term semiconductor. A valence electrons which are

weakly attracted to the nucleus of atoms

A. Valence electrons which are weakly attracted to the nucleus of atoms

B. A material with electrical conductivity in between those and insulators

C. A substance that resists the flow of electric current

D. A large amount of free mobile electrons

3. What is the atomic number of silicon?

A. 10

B. 14

C. 16

D. 32

4. The valence shell in a silicon atom has the number designation of

A. 0

B. 1

C. 2

D. 3

5. What will happen to the depletion region when the terminals are connected as shown in

Figure 1?

p n

Deplition region

Figure 1

A. The depletion region is destroyed.

B. The width of the depletion region increases.

C. The width of the depletion region decreases.

D. The width of the depletion region remains the same.

3 7 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 TUTORIAL QUESTIONS
Multiple-Choice Questions

6. The process of adding impurities to a pure semiconductor material in order to increase its

electrical conductivity is called

A. Velocity

B. Conductivity

C. doping.

D. Permeability

7. The purpose of adding a pentavalent impurity to a semiconductor is to

A. increase the number of free electrons

B. increase the number of holes

C. reduce its electrical conductivity

D. create minority carriers

8. Holes in an n-type semiconductor are

A. minority carriers that are thermally produced

B. minority carriers that are produced by doping

C. majority carriers that are thermally produced

D. majority carriers that are produced by doping

9. A pn junction is formed by

A. the recombination of electrons and holes

B. ionization

C. the boundary of a p-type and an n-type material

D. the collision of a proton and a neutron

10. The depletion region is created by

A. Ionization

B. diffusion

C. recombination

D. answers (A), (B), and (C)

3 8 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 TUTORIAL QUESTIONS

Short-Answer Questions

When a p-n junction is formed, a ___________ region is created on either side of the

junction.

What is meant by the term intrinsic semiconductor?

Explain how a barrier voltage is produced at a p-n junction.

Figure 2 shows the structure for an ___________ atom. The electrons are

___________ charged and the protons are ___________ charged.

+13

Figure 2

When a p-n junction is supplied with a forward biased voltage, what will happen to

a) the width of the depletion region?

b) the junction resistance?

c) the current flow?

When a diode is forward-biased, the current is produced __________holes and

electrons.

Although current is blocked in reverse bias, there is a very ___________ current due

to minority carriers.

A diode is normally operated in the __________________ the ___________________.

For a silicon diode, the value of the forward-bias voltage typically must be greater

than __________________.

When forward biased, a diode __________________.

3 9 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 TUTORIAL QUESTIONS

True/False Questions

1.. An atom is the smallest particle in an element.

TRUE FALSE

2. An electron is a negatively charged particle

TRUE FALSE

3. An atom is made up of electrons, protons, and

TRUE FALSE
neutrons.

4. Electrons are part of the nucleus of an atom.

TRUE FALSE

5. Valence electrons exist in the outer shell of an

TRUE FALSE
atom.

6.Crystals are formed by the bonding of atoms.

TRUE FALSE

7. Silicon is a conductive material.

TRUE FALSE

8. Silicon doped with p and n impurities has one

TRUE FALSE
pn junction.

9. The p and n regions are formed by a process

TRUE FALSE
called ionization.

10. The absence of an electron in the valence

TRUE FALSE
band of an atom is called hole.

4 0 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 TUTORIAL QUESTIONS
Essay Questions

Question 1

a)Define semiconductor.

b)List FIVE (5) types material in semiconductor’s family.

c)State the three categories into which materials can be classified

based on electrical conductivity. Explain how atomic structure

determines the electrical conductivity of these materials.

d) Explain Forward Bias condition when VD>0V which related to the P-N

junction and internal distribution of charge under forward-bias

conditions.

e)State the factors that can free electrons from covalent bonds.

Question 2

a)List all the importance parameter for the atomic structure.

b)Draw and label a p-n junction.

c)By using a suitable diagram, explain how an n-type semiconductor can

be produced.

d)With the aid of diagrams, illustrate the meaning of forward biased and

reverse biased p-n junctions.

e)Illustrate the formation of a P-N junction in terms of:

i.Free electrons mobility

ii.Formation of depletion region and its properties

iii.Existence of threshold voltage and its values for silicon and germanium.

4 1 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 IA L
OR
T
TU
ER
S W
AN
Tutorial answer
pg :10

The atomic number of silicon is 14. This means that there are 14 protons in the

nucleus. Since there is always the same number of electrons as protons in a

neutral atom, there are also 14 electrons.

As you know, there can be up to two electrons in shell 1, eight in shell 2, and

eighteen in shell 3.

Therefore, in silicon there are two electrons in shell 1, eight electrons in shell 2,

and four electrons in shell 3 for a total of 14 electrons. The electron

configuration table for silicon is shown in Table 1.

Notation Explanation

1 st shell 2 electron in 1 shell

2 nd shell 8 electron in 2 shell

3 rd shell 4 electron in 3rd shell

Silicon

4 2 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Tutorial answer
pg :13

Answer

a)What is the basic difference between conductors and insulators?

Conductor Insulator

Conducts electricity Does not conduct

electricity

1-3 valence electrons 5-8 valence electrons

Low resistivity. High resistivity. Atoms

Atoms tend to tend accept

release valence electrons

electrons

Examples: copper, Examples: glass,

silver, aluminum plastics, ceramics

b)

Electrical conductivity intermediate between insulator and conductor

4 valence electrons

Does not easily release or accept electrons

It has negative temperature coefficient

It has small forbidden gap

Examples: silicon, germanium, carbon

c) A conductor such as copper have 1-3 valence electrons.

d) A semiconductor has 4 valence electrons.

e) Three of the best conductive materials is copper, silver and aluminum

4 3 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Tutorial answer
pg :22

a)The purpose of doping process is to produce an extrinsic semiconductor.

b) n-type semiconductor is created when a silicon crystal is doped with

pentavalent impurity

atoms.

c) It has only three valence electrons of the trivalence atoms for doping

process.

d) The minority current carriers in a p-type semiconductor material is the

electrons.

e) A hole exhibits a positive charge.

4 4 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Multiple-choice Question

1. D

2. B

3.B

4.D

5.C

6.C

7.A

8.A

9.C

10.D

4 5 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Short-Answer Questions

1. depletion

2. Intrinsic semiconductor is a pure semiconductor material which does

not contain impurities.

3. The transfer of electrons from the n side of the junction to holes on

the p side of the junction produces a barrier voltage. The barrier voltage

value for silicon is 0.6 to 0.7 V and 0.2 to 0.3 V for germanium.

4. aluminium, negative, positive

5. Area of depletion region: Becomes smaller or thinner

Junction resistance: Decreases

Current flow: Increases

6. Both

7. Small

8. forward-bias region, reverse-bias region

9. 0.7V

10. conducts currents

4 6 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 True/False Questions

1. TRUE

2.TRUE

3. TRUE

4. TRUE

5. TRUE
7. FALSE

6.TRUE
8. TRUE

9. FALSE

10. TRUE

4 7 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Essay Questions

Question 1

a) Semiconductor is a matter between the insulator and conductor. It conducts electricity

better than insulator but poorer than conductors.

b) Five (5) types material in semiconductor’s family.

Silicon,si

Germanium,Ge

Stanum,Sn

Plumbum,Pb

Carbon,C

c) Electrical materials can be classified as conductor, insulator and semiconductor. The

differences between these materials are the number of valence electrons in their atomic

structure. Conductor has one to three valence electrons so atoms tend to release

valence electron. Insulator has five to eight valence electrons. The insulator atom tend to

receive valence electron while semiconductor only has 4 valence electrons. It's not easy to

release or receive valence electron.

d)

i.VD will “pressure” electrons in the n-type material and holes in the p-type material to

recombine with the ions near the boundary and reduce the width of the depletion region.

ii.The resulting minority-carrier flow of electrons from the p -type material to the n-type

material has not changed in but the reduction in the width of the depletion region has

resulted in a heavy majority flow across the junction.

iii.An electron of the n -type material now “sees” a reduced barrier at the junction due to

the reduced depletion region and a strong attraction for the positive potential applied to

the p -type material.

e) Factors that allow electron to become free from covalent bonds are heat,

temperature, potential difference and doping process.

4 8 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Essay Questions

Question 2

a) Atoms consist of three basic particles: protons, electrons, and neutrons. The nucleus

(center) of the atom contains the protons (positively charged) and the neutrons (no charge).

b) p-n junction

c) n-Type semiconductors can be constructed by adding pentavalent impurity atom to the

intrinsic semiconductor. This process is called doping. Pentavalent atoms such as arsenic and

phosphorus have five valence electrons which will provide an extra free electron. So electrons

are majority carrier in n-type material.

d) Forward biased: p-type connected to the positive terminal of supply voltage while n type

connected to the negative terminal.

4 9 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Essay Questions

Reverse biased: p-type connected to the negative terminal of supply voltage while n type

connected to the positive terminal.

e)

i. Free electrons mobility

With the formation of the p and n materials, holes from p ‐ type will diffuse into the n ‐type,

and electrons from n ‐ type will diffuse into the p ‐type. Combination of electrons and holes at

the junction takes place.

ii. Formation of depletion region and its properties

When equilibrium is reached, no further diffusion of electrons and holes across the junction.

This creates the depletion region and has a barrier potential.

The depletion region is a region depleted of any charge carriers.

iii. Existence of threshold voltage and its values for silicon and germanium.

An electric field oriented in the direction from the (+) charge to the (-) charge will be created.

Potential difference across the depletion region occurs and it is called threshold/ knee

voltage (Vk).

Value of Vk for silicon = 0.7 V and germanium = 0.3 V.

5 0 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
REFERENCES
REFERENCES

Albert Malvino, David J Bates (2015). Electronic Principles (7th),

McGraw Hill

Mitchel E. Schultz, (2015). Grob’s Basic Electronics. McGraw Hill

Thomas L. Floyd, (2017). Electronic Devices (Electron Flow Version)

(10th), Pearson

Robert L. Boylestad, Louis Nashelsky (2013). Electronic Devices and

Circuit Theory (11th), Pearson Education

Nurul Asyikin Mad Yusuf,Yusnirah Yusop, Nor Asilah Surip & Yuzi

Saidun (2017). Semiconductor Devices. Oxford Fajar Sdn. Bhd

5 1 | I N T R O D U C T I O N O F S E M I C O N D U C T O R
 Terbitan

TUANKU SULTANAH BAHIYAH