Electronics STE 10

1. Introduction to
Semiconductor Materials

2. A presentation of eSyst.org
Summary
• Course use: DC circuits and/or AC circuits.
Semiconductor devices or solid state courses. In-class
presentation.
• Objective: To provide an early introduction to
semiconductor devices prior to a formal course to reinforce
their importance and their total dominance of electronics
hardware.
• Content: Defines semiconductors and shows basic atomic
structures. Summarizes types of semiconductor materials.
Introduces PN junctions and diodes. Gives an overview of
the concept of a transistor and how it is used in electronics.
A brief introduction to integrated circuits.

3. A presentation of eSyst.org
Student Learning Outcomes
• Upon completion of viewing this presentation, you
should be able to:
– Define conductor, insulator and semiconductor, and
state the resistance or conductance of each.
– Name at least three semiconductor materials and state
the most widely used.
– Name the basic structure of material and explain how it
is formed with atoms.
– Define doping and name the two types of
semiconductor material formed with doping.
– Name the current carriers in N and P-type material.
– Explain how current flows in semiconductor material.

4. Three Major Groups of Materials in
electronics as how they readily allow
charges like electrons to flow through it:
• The goal of electronic materials is to
generate and control the flow of an
electrical current.
• Electronic materials include:
1. Conductors- have low resistance which allows
electrical current flow. Group of materials
which readily pass charges across them.
- A good conductor has 1 valence electrons -
Examples: Aluminum, Copper, Gold Silver and
Zinc

5. 2. Insulators- have high resistance which
suppresses electrical current flow.
-materials which totally prevents charges
from passing through it.
-An insulator has eight valence electrons.
-Examples: Ceramics, Glass, Polyethylene,
rubber, plastic and paper.

6. 3. Semiconductors- can allow or suppress
electrical current flow
-is a material whose properties stand
between conductor and insulator.

7. Conductors
• Good conductors have low resistance so
electrons flow through them with ease.
• Best element conductors include:
– Copper, silver, gold, aluminum, & nickel
• Alloys are also good conductors:
– Brass & steel
• Good conductors can also be liquid:
– Salt water

8. Conductor Atomic Structure
• The atomic structure of
good conductors usually
includes only one
electron in their outer
shell.
– It is called a valence
electron.
– It is easily striped from the
atom, producing current
flow.
Copper Atom

9. Insulators
• Insulators have a high resistance so current
does not flow in them.
• Good insulators include:
– Glass, ceramic, plastics, & wood
• Most insulators are compounds of several
elements.
• The atoms are tightly bound to one another
so electrons are difficult to strip away for
current flow.

10. What is a
Semiconductor?

12. • Semiconductors are materials that
essentially can be conditioned to act as
good conductors, or good insulators, or
any thing in between.
• Examples of Semiconductor materials are
Silicon, Germanium, Gallium Arsenide
etc., where Silicon is the most commonly
used.
• Gallium arsenide stands as the second-
best semiconductor material and is used
in solar cells, laser diodes, microwave
frequency integrated circuits etc.

13. • (Belong to group IV in the Periodic Table of
the Elements. Each atom has four outer
most electrons also called metalloids or 4
valence electrons – an element
intermediate in properties between the
typical metals and nonmetals. It is neither a
good conductor or a good insulator
• Under specific conditions, Semiconductors
have the ability to act either as a pure
conductor or a pure insulator.

14. Semiconductor Valence Orbit
• The main
characteristic of a
semiconductor
element is that it has
four electrons in its
outer or valence
orbit.

15. Semiconductors have brought a revolution in
the field of electronics. Semiconductors are
used for designing electronic components:
• The most commonly used semiconductor
component is the Diode., which allows the
flow of current in one direction only and thus
acts as a one-way electronic valve.
What Are Semiconductors Used For?

16. After the diode, transistor was invented, which
is used for fast switching or current
amplification.
• The invention of diode & transistor opened the
door to nanotechnology and new integrated
chips were designed i.e.
microcontrollers, ULN2003, CD4050 etc.
• All these integrated chips have semiconductor
components embedded in them.
What Are Semiconductors Used For?

18. Types of Semiconductors
Engineers have divided
Semiconductors into two main types,
named:
• Intrinsic Semiconductors.
• Extrinsic Semiconductors.

19. Intrinsic Semiconductors
Semiconductors in their pure form are
called Intrinsic Semiconductors and are
barely useful as they are neither good
conductors nor good insulators.
In the pure forum, the valence shell(of
semiconductor material) carries an equal
number of holes & electrons(silicon has 4
valence electrons).

20. Extrinsic Semiconductors
Impurities(i.e. Boron, Arsenic, Antimony
etc.) are added to the pure Semiconductors by
a method called Doping, which increases
the conductive behavior of
semiconductors and such doped
semiconductors are known as Extrinsic
Semiconductors.
Depending on the doping material used, extrinsic
semiconductors are further divided into two types,
named:

21. N-Type Semiconductors
When a pentavalent(having 5 valence
electrons) material is used as a doping
agent, four of its electrons in the valence
shell create covalent bonds with
the neighboring Si atoms, while the 5th
electron(of pentavalent element) becomes
a free electron. Such extrinsic semiconductors
are called N-Type Semiconductors.
In N-Type Semiconductors, the majority charge
carriers are electrons(negatively charged).

22. N-Type Semiconductors
• Pentavalent Elements normally used in the
doping process are Antimony, Arsenic,
Phosphorous etc.
• As a semiconductor is accepting a free
elector so it is termed as Acceptor, while
the pentavalent element is termed
as Donor as it's donating its electron.

23. N-Type Semiconductors

24. P-Type Semiconductors
• When a semiconductor material is doped with
a Trivalent(having 3 valence
electrons) material, three valence
electrons(of trivalent element)
creates covalent bonds with the Si atoms
nearby but it couldn't provide the 4th electron
and thus creates a hole(positively charged),
which is actually a vacancy & waits for an
electron to join. Such doped semiconductors
are called P-Type Semiconductors.

25. P-Type Semiconductors
• In P-Type Semiconductors, the majority
charge carriers are holes(positively
charged).
• Examples of Trivalent Elements used in the
doping process are Boron, Gallium,
Aluminium, Indium etc.
• The trivalent element is Acceptor here, while
the semiconductor is Donor.

26. P-Type Semiconductors
•

27. Doping of Semiconductors
A semiconductor in its pure form acts as an
insulator as it has an equal number of electrons
and holes in its outermost shell(called the
valence shell).
So, in order to generate conductive properties in
semiconductors, a strictly controlled quantity of
impurity(i.e. arsenic, boron etc.) is added to it and
this method is called Doping.
The intensity of conductive behavior depends on
the type & quantity of impurity added.

28. Two types of impurity elements are
normally, which are:
• Pentavalent: Creates N-Type Semiconductors.
• Trivalent: Creates P-Type Semiconductors.

29. PN Junction in Semiconductors
If a semiconductor material is doped with both
trivalent & pentavalent impurities, then both P-
Type & N-Type regions are created in a single
substance.
As a result, a special barrier is created at the
boundary of these two regions, which stops the
flow of charge carriers and is called the PN
Junction.

30. PN Junction in Semiconductors
This PN Junction formulated the basis of the first
semiconductor component called Diode.
Different variations of PN junction resulted in the
creation of other basic components i.e.
transistor, FET, MOSFET etc.

31. PN Junction in Semiconductors

32. SEMICONDUCTOR MATERIALS
1. Group IV Of Periodic Table
In modern IUPAC notation, it's termed
as Group 14 of the Periodic Table while in
semiconductor circle, it's still considered
as Group IV.
Group IV elements are the most commonly used
semiconductors but few elements of this group
have large band gaps and thus act as insulators.
Semiconductors present in this group
are Carbon, Silicon, Germanium, tin.

33. SEMICONDUCTOR MATERIALS
2. Compound Semiconductors
• Compound Semiconductors are designed by
the chemical combination of two different
elements.
• Compound semiconductors are normally
designed by using elements from Group III & V
of the periodic table.
• Few examples of compound semiconductors
are Gallium Arsenide, Silicon Carbide etc.
•

34. SEMICONDUCTOR MATERIALS
3. Organic semiconductors contain polymer
structures normally composed of carbon or
hydrogen.
The first organic semiconductor discovered
was Bechgaard salt (TMTSF)2PF6 in 1980.

35. SEMICONDUCTOR MATERIALS
4. Liquid/Amorphous Semiconductors
• Normally semiconductors are available in solid-
state but few liquid/amorphous
semiconductors are also discovered
i.e. hydrogenated amorphous silicon.
• Few oxide and alloys also depict
semiconductor behavior.

36. SEMICONDUCTOR MATERIALS

37. Crystal Lattice Structure
• The unique capability
of semiconductor
atoms is their ability to
link together to form a
physical structure
called a crystal lattice.
• The atoms link
together with one
another sharing their
outer electrons.
• These links are called
covalent bonds.
2D Crystal Lattice Structure

38. 3D Crystal Lattice Structure

39. A presentation of eSyst.org
Semiconductors can be Insulators
• If the material is pure semiconductor material like
silicon, the crystal lattice structure forms an excellent
insulator since all the atoms are bound to one another
and are not free for current flow.
• Good insulating semiconductor material is referred to
as intrinsic.
• Since the outer valence electrons of each atom are
tightly bound together with one another, the electrons
are difficult to dislodge for current flow.
• Silicon in this form is a great insulator.
• Semiconductor material is often used as an insulator.

40. Doping
• To make the semiconductor conduct electricity,
other atoms called impurities must be added.
• “Impurities” are different elements.
• This process is called doping.

41. Semiconductors can be Conductors
• An impurity, or element
like arsenic, has 5
valence electrons.
• Adding arsenic (doping)
will allow four of the
arsenic valence
electrons to bond with
the neighboring silicon
atoms.
• The one electron left
over for each arsenic
atom becomes available
to conduct current flow.

42. Resistance Effects of Doping
• If you use lots of arsenic atoms for doping,
there will be lots of extra electrons so the
resistance of the material will be low and
current will flow freely.
• If you use only a few boron atoms, there will
be fewer free electrons so the resistance will
be high and less current will flow.
• By controlling the doping amount, virtually
any resistance can be achieved.

43. Another Way to Dope
• You can also dope a
semiconductor material with an
atom such as boron that has
only 3 valence electrons.
• The 3 electrons in the outer orbit
do form covalent bonds with its
neighboring semiconductor
atoms as before. But one atom
is missing from the bond.
• This place where a fourth
electron should be is referred to
as a hole.
• The hole assumes a positive
charge so it can attract electrons
from some other source.
• Holes become a type of current
carrier like the electron to
support current flow.

44. Types of Semiconductor Materials
• The silicon doped with extra electrons is
called an “N type” semiconductor.
– “N” is for negative, which is the charge of an
electron.
• Silicon doped with material missing
electrons that produce locations called holes
is called “P type” semiconductor.
– “P” is for positive, which is the charge of a hole.

45. Current Flow in N-type Semiconductors
• The DC voltage source has
a positive terminal that
attracts the free electrons in
the semiconductor and pulls
them away from their atoms
leaving the atoms charged
positively.
• Electrons from the negative
terminal of the supply enter
the semiconductor material
and are attracted by the
positive charge of the atoms
missing one of their
electrons.
• Current (electrons) flows
from the positive terminal to
the negative terminal.

46. A presentation of eSyst.org
Current Flow in P-type Semiconductors
• Electrons from the
negative supply terminal
are attracted to the
positive holes and fill them.
• The positive terminal of the
supply pulls the electrons
from the holes leaving the
holes to attract more
electrons.
• Current (electrons) flows
from the negative terminal
to the positive terminal.
• Inside the semiconductor
current flow is actually by
the movement of the holes
from positive to negative.

47. In Summary
• In its pure state, semiconductor material is an excellent
insulator.
• The commonly used semiconductor material is silicon.
• Semiconductor materials can be doped with other atoms to
add or subtract electrons.
• An N-type semiconductor material has extra electrons.
• A P-type semiconductor material has a shortage of
electrons with vacancies called holes.
• The heavier the doping, the greater the conductivity or the
lower the resistance.
• By controlling the doping of silicon the semiconductor
material can be made as conductive as desired.