EEE231- Electronics-1 Lecture 01 Delivered at Comsats Institute of Information Technology Islamabad (CIIT)

1. EEE231
Electronics 1
Lecture 1
Course Introduction
&
Basic Concepts

2. Instructor Details
(Muhammad Rizwan Azam)
• Educational Background
o PHD .. (Control Systems)
o MS (Control Systems)
o BSc Eng. (Electronics)
• Contact Details
o Room # 113, EE Block
o rizwan.azam@comsats.edu.pk

3. Course Prerequisites
1. Electric Circuit analysis 1 (EEE 121)
2. Calculus and Analytic Geometry (MTH104)
3. Applied Physics

4. Marks Distribution (Theory)
Sessional -1 10%
Sessional 2 15%
Quizzes (4) 15%
Assignments (4) 10%
Terminal Exam 50%
Note:
Quizzes will be announced as well un announced.
Expect a quiz after submission of assignment.
Copied assignments and assignments submitted after the due
date will be marked zero.

5. Course Objectives
1. To make students understand construction, physical
characteristics and operation of the major semiconductor
devices.
2. To study, analyze and design circuits using semiconductor
devices.
3. To illustrate how the device characteristics are utilized in
switching, digital, and amplification applications.

6. Topics to be Covered
1) Semiconductor material and properties
2) Diode model, equivalent model and circuit analysis
3) Analysis of diode based circuits (rectifiers, clipper,
clampers, etc.)
4) Special diodes characteristics and applications
5) Bipolar transistors characteristics and modes of operations
6) DC analysis, dc load line, biasing of bipolar transistor
circuits
7) Small signal analysis of bipolar transistor circuits
8) Design and analysis of common bipolar transistor
amplifiers

7. Course Material
• Textbooks:
o Electronic Circuits Analysis and Design, 3rd Edition, by Donald A
Neamen.
o Electronic devices and circuit theory, 10th ed. Boylestad.
• Reference Books:
o Electronic Devices 7th (or 9th ) Edition by Floyd.
o Electronics Devices and Circuits, 6th Edition by Bogart.
o Introductory Electronic Devices and Circuits, 4th Edition by
Robert T. Paynter.
o Microelectronic Circuits 6th Edition by Sedra, Smith.

8. Why Electronics ?
• The giant strides that we have made in the areas of
communications and computers are possible only because of
the great successes that we have achieved in the field of
electronics.

9. Some Basic Concepts
• Electronics :
o Science of the motion of charges in a gas, vacuum, or
semiconductor.
• Ohm’s Law:
o The current through a conductor is directly proportional to the
potential difference.
𝑉 = 𝐼 ∗ 𝑅
• Electrical Power:
o Power is how much work is done over time.
𝑃 = 𝑉 ∗ 𝐼

10. AC and DC
• Direct Current (DC):
o Flow of charge in one direction,
o Current maintains the same polarity,
o DC is produced by sources such as batteries, solar cells etc.
• Alternating Current (AC):
o An alternating voltage source periodically alternates or reverses
in polarity.
o The resulting current, therefore, periodically reverses in
direction.

11. Electronic Circuits
• In most electronic circuits
o There are two inputs.
o One input is from a power supply that provides dc voltages and
currents to establish the proper biasing for the circuit.
o The second input is a signal that can be amplified by the circuit.
o The output signal can be larger than the input signal.

12. Analog and Digital Signals
• Analog Signals
o The magnitude of an analog signal may have any value.
o The amplitude may vary continuously with respect to time.
o Electronic circuits that process such signals are called analog
circuits.

13. Analog and Digital Signals
• Digital Signals
o An alternative signal is at one of two distinct levels and is called
a digital signal.
o The digital signal has discrete values, it is said to be quantized.
o Electronic circuits that process digital signals are called digital
circuits.

14. Atom
• An atom is composed of ;
o A nucleus, which contains positively charged protons and neutral
neutrons,
o And negatively charged electrons that, orbit the nucleus.
• The electrons are distributed in various “shells” at
different distances from the nucleus,
• Electron energy increases as shell
radius increases.
• Electrons in the outermost shell
are called valence electrons,

15. Electronic Materials
• The basic goal of electronic materials is to generate
and control the flow of an electric current.
• Electronic materials include:
o Conductors: have low resistance which allows electric
current flow
o Insulators: have high resistance which suppresses electric
current flow
o Semiconductors: can allow or suppress electrical current flow

16. Insulators
• Insulators have a high resistance so current does not flow
in them.
• Have 8 valence electrons
• Good insulators include:
o 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.

17. Insulators
Insulators have tightly bound electrons in their outer shell
These electrons require a very large amount of energy to free
them for conduction
Let’s apply a potential difference across the insulator above…
The force on each electron is not enough to free it from its orbit
and the insulator does not conduct
Insulators are said to have a high resistivity / resistance

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

19. Conductors
Conductors have loosely bound electrons in their outer shell
These electrons require a small amount of energy to free them
for conduction
Let’s apply a potential difference across the conductor above…
The force on each electron is enough to free it from its orbit and
it can jump from atom to atom – the conductor conducts
Conductors are said to have a low resistivity / resistance

20. 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

21. Semiconductors
• A material whose properties are such that it is not
quite a conductor, not quite an insulator.
• Semiconductors have a resistivity/resistance between
that of conductors and insulators.
• Their electrons are not free to move but a little energy
will free them for conduction
• Some common semiconductors
o elemental
• Si - Silicon (most common)
• Ge - Germanium
o compound
• GaAs - Gallium arsenide
• GaP - Gallium phosphide
• AlAs - Aluminum arsenide
• AlP - Aluminum phosphide
• InP - Indium Phosphide
(The resistance of a semiconductor decreases as the
temperature increases – Negative Temp. Coefficient)

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

23. 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 valence electrons are
shared between atoms,
forming what are called
covalent bonds.
2D Crystal Lattice
Structure

24. The Silicon (Si) Atom
Silicon has a valency
of 4 i.e. 4 electrons in
its outer shell
Each silicon atom
shares its 4 outer
electrons with 4
neighbouring atoms
These shared electrons
– bonds – are shown as
horizontal and vertical
lines between the
atoms
This picture shows the
shared electrons

25. Silicon – the crystal lattice
If we extend this
arrangement
throughout a piece of
silicon…
We have the crystal
lattice of silicon
This is how silicon
looks when it is cold,
i.e. T = 0 K
It has no free electrons – it cannot conduct electricity – therefore it
behaves like an insulator

26. Energy Bands
• When silicon atoms come together to form a crystal, the
electrons occupy particular allowed energy bands.
• Minimum energy required to break the covalent bond is
Bandgap Energy (𝐸𝑔).
𝐸𝑔 = 𝐸𝑐 − 𝐸 𝑣
Free
Electrons
Electrons Can
not exist here

27. Electron Hole Pair
• When an electron jumps to the conduction band, a
vacancy is left in the valence band within the crystal. This
vacancy is called a hole.

28. Electron Movement in Silicon
However, if we apply
a little heat to the
silicon….
An electron may gain
enough energy to
break free of its
bond…
It is then available
for conduction and is
free to travel
throughout the
material

29. Hole Movement in Silicon
Let’s take a closer
look at what the
electron has left
behind
There is a gap in the
bond – what we call
a hole

30. Hole Movement in Silicon
This hole can also
move…
An electron – in a
nearby bond – may
jump into this hole…
Effectively causing
the hole to move…
Like this…
In semiconductors, the negatively
charged free electron, and the positively
charged hole contribute to the current.

31. Doping
• Relying on heat or light for conduction does not make
reliable electronics.
• To make the semiconductor conduct electricity, other
atoms called impurities must be added.
• “Impurities” are different elements, normally from III
or V group of periodic table.
• This process is called doping.

32. Semiconductor Types
• An intrinsic semiconductor, also called an undoped
semiconductor or i-type semiconductor, is a pure
semiconductor without any significant dopant species
present.
• Since the electron and hole concentrations in an intrinsic
semiconductor are relatively small.
• These concentrations can be greatly increased by adding
controlled amounts of certain impurities (Doping).
• An extrinsic semiconductor is a semiconductor that has
been doped.

33. 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.

34. The Phosphorus Atom
Phosphorus is
number 15 in the
periodic table
It has 15 protons and
15 electrons – 5 of
these electrons are in
its outer shell

35. Doping – Making n-type Silicon
Suppose we remove
a silicon atom from
the crystal lattice…
and replace it with a
phosphorus atom
We now have an electron that is not bonded – it is thus free for
conduction

36. Doping – Making n-type Silicon
Let’s remove another
silicon atom…
and replace it with a
phosphorus atom
As more electrons
are available for
conduction we have
increased the
conductivity of the
material
If we now apply a potential difference
across the silicon…
Phosphorus is called
the dopant, or donor
impurity,

37. Extrinsic Conduction – n-type Silicon
A current will flow
Note:
The negative
electrons move
towards the positive
terminal

38. From now on
n-type will be
shown like
this.N-type Silicon
• This type of silicon is called n-type
• This is because the majority charge carriers are
negative electrons
• A small number of minority charge carriers – holes –
will exist due to electrons-hole pairs being created in
the silicon atoms due to heat
• The silicon is still electrically neutral as the number
of protons is equal to the number of electrons

39. The Boron Atom
Boron is number 5
in the periodic table
It has 5 protons and
5 electrons – 3 of
these electrons are
in its outer shell

40. Doping – Making p-type Silicon
As before, we
remove a silicon
atom from the crystal
lattice…
This time we replace
it with a boron atom
Notice we have a
hole in a bond – this
hole is thus free for
conduction

41. Doping – Making p-type Silicon
Let’s remove another
silicon atom…
and replace it with
another boron atom
As more holes are
available for
conduction we have
increased the
conductivity of the
material
If we now apply a potential difference
across the silicon, hole current starts to
flow.
Boron is the dopant
here, also called
acceptor impurity.

42. P-type Silicon
• This type of silicon is called p-type
• This is because the majority charge carriers are positive
holes
• A small number of minority charge carriers – electrons –
will exist due to electrons-hole pairs being created in the
silicon atoms due to heat
• The silicon is still electrically neutral as the number of
protons is equal to the number of electrons
From now on
p-type will be
shown like
this.

43. The p-n Junction
Suppose we join a piece of p-type silicon to a piece of n-
type silicon
We get what is called a p-n junction
Remember – both pieces are electrically neutral

44. The p-n Junction
When initially joined
electrons from the n-
type migrate into the p-
type – less electron
density there
When an electron
fills a hole – both the
electron and hole
disappear as the gap
in the bond is filled
This leaves a region with no free charge carriers – the depletion
layer – this layer acts as an insulator

45. The p-n Junction
As the p-type has
gained electrons – it
is left with an overall
negative charge…
As the n-type has
lost electrons – it is
left with an overall
positive charge…
Therefore there is a voltage across the junction – the junction
voltage – for silicon this is approximately 0.6 V
0.6 V

46. The Reverse Biased P-N Junction
Take a p-n junction
Apply a voltage
across it with the
p-type negative
n-type positive
Close the switch
The voltage sets
up an electric
field throughout
the junction The junction is said to be reverse – biased

47. The Reverse Biased P-N Junction
Negative electrons
in the n-type feel
an attractive force
which pulls them
away from the
depletion layer
Positive holes in
the p-type also
experience an
attractive force
which pulls them
away from the
depletion layer
Thus, the depletion layer ( INSULATOR ) is
widened and no current flows through the
p-n junction

48. The Forward Biased P-N Junction
Take a p-n junction
Apply a voltage
across it with the
p-type postitive
n-type negative
Close the switch
The voltage sets
up an electric
field throughout
the junction
The junction is said to be
forward – biased

49. The Forward Biased P-N Junction
Negative electrons
in the n-type feel a
repulsive force
which pushes
them into the
depletion layer
Positive holes in
the p-type also
experience a
repulsive force
which pushes them
into the depletion
layer
Therefore, the depletion layer is eliminated
and a current flows through the p-n junction

50. The Forward Biased P-N Junction
At the junction
electrons fill holes
They are
replenished by the
external cell and
current flows
Both disappear
as they are no
longer free for
conduction
This continues as long as the external voltage
is greater than the junction voltage i.e. 0.6 V

51. The Forward Biased P-N Junction
If we apply a
higher voltage…
The electrons feel
a greater force
and move faster
The current will
be greater and
will look like
The p-n junction is called a DIODE
and is represented by the symbol…
The arrow shows the
direction in which it
conducts current
this….