Basic Electronics
SPS 3200
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.
The pn junction
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Quiz
1. A semiconductor is a crystalline material with
a. many free electrons held by the attraction of positive ions
b. strong covalent bonds between neighboring atoms
c. only one electron in its outer shell
d. a filled valence shell
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Quiz
1. A semiconductor is a crystalline material with
a. many free electrons held by the attraction of
positive ions
b. strong covalent bonds between neighboring atoms
c. only one electron in its outer shell
d. a filled valence shell
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Quiz Quiz
2. A metallic conductor has
a. many free electrons held by the attraction of
positive ions
b. covalent bonds between neighboring atoms
c. four electrons in its outer shell
d. a filled valence shell
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Quiz Quiz
3. In a semiconductor, the concept of an energy gap is
used to show the difference between the energies of the
a. nucleus and outer shell electrons
b. nucleus and the free electrons
c. conduction band electrons and valence electrons
d. core electrons and valence electrons
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Quiz Quiz
4. An impurity such as Antimony (Sb) has five electrons
in its outer shell. When silicon has Sb impurities,
a. an n material is formed
b. the crystal will be negatively charged
c. both of the above
d. none of the above
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Quiz Quiz
5. Compared to a p-material, the energy levels in an n-
material are
a. the same
b. greater
c. lower
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Quiz Quiz
6. When a pn junction is formed, electrons move across
the junction and fill holes in the p-region. The filled hole
is a
a. neutral atom
b. minority carrier
c. positive ion
d. negative ion
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
Quiz Quiz
Answers:
1. b 6. d
2. a
3. c
4. a
5. c
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
eNd
• Next Lecture ,
Chapter 2 Diodes and Application
Electronic Devices, 9th edition © 2012 Pearson Education. Upper Saddle River, NJ, 07458.
Thomas L. Floyd All rights reserved.
