1. Principles & Applications
Electronics
Principles & Applications
Sixth Edition
Charles A. Schuler
Chapter 2
Semiconductors
© Glencoe/McGraw-Hill

2. INTRODUCTION Semiconductors N-type Semiconductors
Conductors and Insulators
Semiconductors
N-type Semiconductors
P-type Semiconductors
Majority and Minority Carriers

3. A nucleus also has protons and they have a positive charge.
Most atoms have neutrons which have no charge.
A nucleus also has protons
and they have a positive charge.
The center of an atom is called the nucleus.
Negative electrons
orbit the nucleus.

4. This is a copper atom. Its net charge = 0. Valence electron
It has 29 protons. N N N N
It has 29 electrons.
This is a copper atom.
Its net charge = 0.

5. The valence electron is the important feature.
Its attraction to the nucleus is relatively weak.

6. A simple model of the copper atom looks like this:
The valence electron
The nucleus plus the inner electron orbits

7. attracted to the nuclei. to conduct electricity
Remember, the valence
electrons are weakly
attracted to the nuclei.
Copper wire is used
to conduct electricity
because the valence
electrons move freely
through its structure.

8. It acts as an electrical insulator.
So far, we know that copper’s single valence
electron makes it a good conductor.
The rule of eight states that a material like this
would be stable since its valence orbit is full.
No Vacancy
It acts as an electrical insulator.

9. Atomic Quiz
The dense and central part of any atom is called the ________.
nucleus
Atom net charge is 0 since the number of protons equals the number of ______.
electrons
The outermost orbit of all atoms is called the ________ orbit.
valence
Good electrical conductors have free
valence ________.
electrons
The magic number for valence stability
is ________.
eight

10. Atoms of the same type can join together and form covalent bonds.
This is an electron sharing process.
Silicon atoms have four valence electrons.

11. The covalent sharing satisfies the rule of eight.
In this structure, one bond is formed with each neighbor.

12. This is a silicon crystal.
It does not conduct because its valence
electrons are captured by covalent bonds.

13. Covalent bonds can be broken by heating a silicon crystal.
Free electron
Hole
Thermal carriers

14. The thermal carriers support the flow of current.

15. Heating silicon crystals to make them conduct is not practical!

16. Each donor atom that enters the crystal adds a free electron.
A silicon crystal can be doped with a donor impurity.
Free electron 5 1 4
This is an arsenic atom.
Each donor atom that enters the
crystal adds a free electron. 2 3

17. Silicon that has been doped with arsenic is called N-type.
The free electrons in N-type silicon support the flow of current.

18. Each acceptor atom that enters the
A silicon crystal can be doped with an acceptor impurity.
Hole 1
This is a boron atom.
Each acceptor atom that enters the
crystal creates a hole. 2 3

19. Silicon that has been doped with boron is called P-type.
The holes in P-type silicon support the flow of current.

20. What are two practical methods of making silicon semiconduct?
Free electron
Hole
(N-type)
(P-type)
Add a pentavalent
impurity.
Add a trivalent
impurity.

21. This is a P-type crystal.
Due to heat, it could have a few free electrons.
These are called minority carriers.

22. This is an N-type crystal.
Due to heat, it could have a few free holes.
These are called minority carriers.

23. Silicon is the workhorse of the semiconductor industry but compound semiconductors help out in key areas.
Gallium arsenide
Indium phosphide
Mercury cadmium telluride
Silicon carbide
Cadmium sulfphide
Cadmium telluride

24. Semiconductor Quiz A pure silicon crystal, at room temperature,
acts as an electrical ________.
insulator
The current carriers, in N-type silicon, are called ________.
electrons
The current carriers, in P-type silicon, are
called ________.
holes
The minority carriers, in N-type silicon, are
called ________.
holes
The minority carriers, in P-type silicon, are
called ________.
electrons

25. REVIEW Conductors and Insulators Semiconductors N-type Semiconductors
P-type Semiconductors
Majority and Minority Carriers