Chapter One Introduction to Electronics

Dr. Derar Mraiziq

Content

▪ The Atom
▪ Material Used in Electronics
▪ Current in Semiconductors
▪ N-Type & P-Type Semiconductors
▪ The PN Junction

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
The Atom

• An atom is the smallest particle of an element

that retains the characteristics of that element.
• Each of the known 118 elements has atoms that
are different from the atoms of all other
elements.
• This gives each element a unique atomic
structure.

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Bohr Atom

The Bohr model of the atom is that electrons

can circle the nucleus only in specific orbits,
which correspond to discrete energy levels
called shells.
Energy

The atomic number is the number

of protons in the nucleus.

The outermost occupied shell

is called the valence shell and
electrons that occupy this shell
are called valence electrons. Nucleus Shell 1

Shell 2
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Bohr Atom

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Bohr Atom

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Material Used in Electronics

Conductors

Materials can be classified by their ability to conduct

electricity. This ability is related to the valence electrons.

Core (+1)
Copper is an example of an
excellent conductor. It has only
one electron in its valence band,
which can easily escape to the
conduction band, leaving behind a +29
positive ion (the core). Like all
metals, copper has many free
electrons which are loosely held
by the attraction of the positive
metal ions.
Material Used in Electronics
Insulators

Insulators have tightly bound electrons with few

electrons available for conduction.
Nonmetals, such as glass, air, paper, and rubber are excellent
insulators and widely used in electronics. Even these materials can
break down and conduct
electricity if the voltage is
high enough.
Material Used in Electronics
Semiconductors

Semiconductors are between conductors and insulators

in their ability to conduct electricity.
Core (+4)
Silicon is an example of a single
element semiconductor. It has four
+14
electrons in its valence band.

+4

Unlike metals, silicon forms strong covalent

bonds (shared electrons) with its neighbors. +4 +4 +4

Intrinsic silicon is a poor conductor because most

of the electrons are bound in the crystal and take
+4
part in forming the bonds between atoms.
Material Used in Electronics

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
 Material Used in Electronics

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Band Gap

▪ When an electron acquires enough additional

energy, it can leave the valence shell, become a
free electron, and exist in what is known as the
conduction band
▪ The difference in energy between the valence
band and the conduction band is called an
energy gap or band gap.
▪ Once in the conduction band, the electron is free
to move throughout the material and is not tied
to any given atom

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Band Gap

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Current in Semiconductors
Semiconductors

In intrinsic silicon, a few electrons can jump

the energy gap between the valence and
conduction band. Having moved into the
conduction band, a “hole” (vacancy) is left in
the crystal structure.
Conduction Free
band electron
Energy gap Heat
Energy
Valence Hole
band
Electron-hole pair
Current in Semiconductors
Semiconductors
Within the crystalline structure, there are two types of charge
movement (current):
1) The conduction band electrons are free to move under the influence of an
electric field. (electron Current )
Current in Semiconductors
2) The bound (valence) electrons move between atoms,
effectively moving holes from one atom to another as
illustrated. Holes act like positive charges, with their own
mobility.

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
N-Type & P-Type Semiconductors

▪ Semi-conductive materials do not conduct

current well.
▪ This is because of the limited number of free
electrons in the conduction band and holes in
the valence band.
▪ Semiconductors conductivity can be drastically
increased by the controlled addition of impurities
to the intrinsic pure.

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Doping Process

▪ Doping process , increases the number of

current carriers (electrons or holes).
▪ The two categories of impurities are n-type
and p-type.

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
N-Type Semiconductors

▪ To increase the number of conduction-band

electrons in intrinsic silicon, pentavalent
)‫ (خماسي التكافؤ‬impurity atoms are added.

▪ These are atoms with five valence electrons

such asarsenic (As), Phosphorus (P),
bismuth (Bi), and antimony (Sb)

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
N-Type Semiconductors

Since most of the current carriers are

electrons, silicon (or germanium)
doped with pentavalent atoms is an
n-type semiconductor (the n stands
for the negative charge on an
electron)

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
P-Type Semiconductors

▪ To increase the number of holes in intrinsic

silicon, trivalent impurity atoms are added.
▪ These are atoms with three valence
electrons such as boron (B), indium (In), and
gallium (Ga)

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
P-Type Semiconductors

The p stands for the positive

charge on an holes )

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
The pn junction

▪ Take a block of silicon and dope part of it

with a trivalent impurity and the other part
with a pentavalent impurity, a boundary
called the pn junction is formed.
▪ The pn junction is the basis for diodes,
certain transistors, solar cells, and other
devices

Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.