This document discusses different types of solids and semiconductors. It describes conductors as mostly metals, insulators as mostly nonmetals, and semiconductors as metalloids with an intermediate-sized band gap between the valence and conduction bands. Semiconducting elements like silicon and germanium are the basis for solid-state electronic devices, and their conductivity increases when doped with small amounts of other elements to become either n-type or p-type semiconductors. Joining an n-type and p-type semiconductor produces a p-n junction that can function as a rectifier, allowing current to flow in only one direction.

1. Solids: Conductors, Insulators and
Semiconductors
• Conductors: mostly metals
• Insulators: mostly nonmetal materials
• we’ll study allotropes of carbon and study their
properties
• Semiconductors: metalloids
1

2. Solids: Conductors, Insulators and
Semiconductors
2
Conductor Insulator Semiconductor
Valence Band
in red
Conduction Band: white
Band gap
No gap

3. Solids: Conductors, Insulators and
Semiconductors
3
Conductor Insulator
Band gap = 5.5 eV
≈ 530 kJ/mol
No gap
Graphite
Diamond

4. Solids: Conductors, Insulators and
Semiconductors
4
Semiconductor
Band gap
Band Gap for Semiconductors
Diamond 5.5 eV
Si 1.1 eV
Ge 0.67 eV

5. Semiconductors
• Metalloids: semiconducting elements
• low electrical conductivity at room
temperature
• Electrical conductivity increases with temp.
• Gap between valence and conduction band is
intermediate in size
5

6. Semiconductors
• Semiconducting elements form the basis of solid
state electronic devices.
6
– A striking property of these elements is that their
conductivities increase markedly when they are
doped with small quantities of other elements.
– Metalloids (such as silicon or germanium) are
semiconducting elements whose electrical
conductivity increases as temperature increases.

7. Semiconductors
• Semiconducting elements form the basis of solid
state electronic devices.
7
– When silicon is doped with boron, it
becomes a p-type semiconductor, in
which an electrical current is carried by
positively charged holes

8. Semiconductors
• Semiconducting elements form the basis of solid
state electronic devices.
8
– Joining a p-type semiconductor to an n-
type semiconductor produces a p-n
junction, which can function as a rectifier.
– A rectifier is a device that allows current to
flow in one direction, but not the other.

9. Figure 13.30:
A p-n junction as a
rectifier.
9

10. Slide 5
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Semiconductor Materials
Common materials used in the development of semiconductor
devices:
• Silicon (Si)
• Germanium (Ge)

11. Slide 6
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Doping
The electrical characteristics of Silicon and Germanium are improved
by adding materials in a process called doping.
The additional materials are in two types:
• n-type
• p-type

12. Slide 7
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
n-type materials make the Silicon (or Germanium) atoms more
negative-type materials make the Silicon (or Germanium) atoms more
positive.
Join n-type and p-type doped Silicon (or Germanium) to form a p-n
junction.
n-type versus p-type

13. Slide 8
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
p-n junction
When the materials are joined, the negatively charged atoms of the n-
type doped side are attracted to the positively charged atoms of the p-
type doped side.
The electrons in the n-type material migrate across the junction to the p-
type material (electron flow).
Or you could say the ‘holes’ in the p-type material migrate across the
junction to the n-type material (conventional current flow).
The result is the formation of a depletion layer around the junction.
depletion
layer
p n

14. Slide 9
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Operating Conditions
• No Bias
• Forward Bias
• Reverse Bias

15. Slide 10
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
No external voltage is applied: VD = 0V and no current is flowing ID =
0A.
Only a modest depletion layer exists.
No Bias Condition

16. Slide 11
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Reverse Bias Condition
External voltage is applied across the p-n junction
in the opposite polarity of the p- and n-type materials.
This causes the depletion layer to widen.
The electrons in the n-type material are attracted
towards the positive terminal and the ‘holes’ in
the p-type material are attracted towards the
negative terminal.

17. Slide 12
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Forward Bias Condition
External voltage is applied
across the p-n junction in the
same polarity of the p- and n-
type materials.
The depletion layer is narrow.
The electrons from the n-type
material and ‘holes’ from the p-
type material have sufficient
energy to cross the junction.

18. Slide 28
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
An ohmmeter set on a low ohm's scale can be used to test a diode.
A normal diode will have the following readings.
The diode should be tested out of circuit.
B. Ohmmeter

19. Slide 30
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Other Types of Diodes
1. Zener Diode2. Light Emitting Diode
3. Diode Arrays

20. Slide 31
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
A Zener is a diode operated in reverse bias at the Peak Inverse Voltage (PIV)
called the Zener Voltage (VZ).
Symbol
Common Zener Voltages: 1.8V to 200V
1. Zener Diode

21. Slide 32
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
2. Light Emitting Diode (LED)
This diode when forward biased emits photons. These can be in the visible
spectrum.
Symbol
The forward bias voltage is higher, usually around 2-3V.

22. Slide 33
Robert BoylestadDigital Electronics Copyright ©2002 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Multiple diodes can be packaged together in an integrated circuit (IC).
A variety of combinations exist.
Example of an array:
3. Diode Arrays