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Lecture # 01
Course: ETE 107 Electronics 1
Course Instructor: Rashedul Islam
Outlines:
• Introduction to Electronics, Voltage, Current,
Resistance & Power
• Conductors, Insulators & Semiconductors
• Intrinsic & Extrinsic Semiconductors
• P Type & N Type Semiconductor Materials, P-N
Junctions
• Operational Principle of P-N Junction Diode
• Forward & Reverse Bias
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What is Electronics:
• Electronics is the division of science,
engineering & technology that deals with
electronic components, their characteristics
and operational methods.
• Examples of Electronic Components are:
Diodes, Transistors, Amplifiers and many more
semiconductor devices.
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Voltage, Current, Resistance & Power:
• Voltage is the pressure/force which causes the
electrons to be moved. The Unit for measuring the
Voltage is Volt.
• Current is the result/output of the movement or flow
of Electrons. The unit for measuring the current is
Ampere.
• Resistance is the ability of opposing the flow of
Electrons (Current). It is measured in Ohm.
• Lastly, Power is the multiplication of Voltage & Current.
That means Power is the rate in which electric energy
transferred in any electric circuit. The unit of Power
measurement is Watt.
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Conductor:
• A Conductor is a material which contains
movable electronic charges. Here,
electronic charges can be either positive
charge (e.g. Holes) or negative charge (e.g.
Electrons).
• Inside a Conductor a free electronic charge
can move freely and thus provides us
Electronic Current.
• The term conductor is also used
interchangeably for indicating Wires.
• Example: Copper, Aluminum etc.
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Insulator:
• An Insulator is a material which contains very strongly bonded electrons
with nuclear in atoms and does not have any free electrons to move
• Opposite characteristics than that of a conductor
• Example: Glass, Wood, Plastic etc.
Semiconductor:
• Semiconductors are materials which has electrical conductivity
intermediate between Conductor & Insulator.
• In normal condition, it acts like an Insulator. But its conductivity varies in
Temperature, Optical Excitations or Impurity contents.
• It non-linear Current-Voltage Characteristics
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Intrinsic & Extrinsic Semiconductors:
• A perfect semiconductor material with no
impurities or lattice defects is called an Intrinsic
Semiconductor material. Examples: Pure Silicon,
Gallium Arsenide.
• On the other hand a semiconductor material in
which impurities has been put-in intentionally is
called an Extrinsic Semiconductor Material.
Examples: P-Type & N-Type Semiconductors.
• The Process of putting impurities inside an
intrinsic semiconductor is called Doping.
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P-Type Semiconductors:
• Whenever by doing Doping process, positive electrical charge is
increased in a pure semiconductor device, it is then called P-Type
Semiconductors.
• Group III elements (e.g. Boron, gallium) in periodic tables are used
for making P-type semiconductors
N-Type Semiconductors:
• Whenever by doing Doping process, negative electrical
charge is increased in a pure semiconductor device, it is
then called N-Type Semiconductors.
• Group V elements (e.g. Phosphorus, Arsenic) in periodic
tables are used for making P-type semiconductors
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P-N Junctions:
• When a junction of P-type & N-type material
is created in a single crystal semiconductor
materials, it is called P-N Junction.
• Different Processes such as ION Implantation,
Diffusion, Doping are used to create P-N
Junctions.
• P–N junctions are elementary "building
blocks" of many semiconductor electronic
devices such as diodes, transistors, solar cells,
LEDs, and integrated circuits;
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Operational Principle of P-N Junction Diode
To understand how a pnjunction diode works, begin
by imagining two separate bits
of semiconductor, one n-type,
the other p-type
Bring them together and join
them to make one piece of
semiconductor
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Operational Principle of P-N Junction Diode
Free electrons on the n-side and
free holes on the p-side can
initially wander across the
junction. When a free electron
meets a free hole it can 'drop into
it'. So far as charge movements
are concerned this means the
hole and electron cancel each
other and vanish.
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Operational Principle of P-N Junction Diode
As a result, the free electrons and
holes near the junction tend to eat
each other, producing a region
depleted of any moving charges.
This creates what is called the
depletion zone.
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Operational Principle of P-N Junction Diode
Now, any free charge which wanders into
the depletion zone finds itself in a region
with no other free charges. Locally it sees
a lot of positive charges (the donor
atoms) on the n-type side and a lot of
negative charges (the acceptor atoms) on
the p-type side. These exert a force on
the free charge, driving it back to its 'own
side' of the junction away from the
depletion zone.
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Operational Principle of P-N Junction Diode
The acceptor and donor atoms are 'nailed
down' in the solid and cannot move around.
However, the negative charge of the
acceptor's extra electron and the positive
charge of the donor's extra proton (exposed
by it's missing electron) tend to keep the
depletion zone swept clean of free charges
once the zone has formed. A free charge
now requires some extra energy to
overcome the forces from the
donor/acceptor atoms to be able to cross
the zone. The junction therefore acts like a
barrier, blocking any charge flow (current)
across the barrier.
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Forward & Reverse Bias:
An external voltage applied to a PN junction is called BIAS.
If, for example, a battery is used to supply bias to a PN junction and is
connected so that its voltage opposes the junction field, it will reduce the
junction barrier and, therefore, aid current flow through the junction.
This type of bias is known as forward bias, and it causes the junction to
offer only minimum resistance to the flow of current.
If the battery mentioned earlier is connected across the junction so that
its voltage aids the junction, it will increase the junction barrier and
thereby offer a high resistance to the current flow through the junction.
This type of bias is known as reverse bias
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