Unit 5
Basics of Electronics
Introduction
Electronic devices are devices that made from conductors and insulators and execute their
purpose electrically. Now a day, our daily lives are dependent on electronics. For example:
calculators, digital watches, mobile phones, televisions, and computers are just some of the
electronic devices that we use every day because, they simplify our activities. Electronics plays
an important role in different fields. For example, equipments in the aerospace industry, in the
automobile industries, in medicine [such as magnetic resonance imaging (MRI), computed
tomography (CT) and X-rays] rely on electronics in order to do their work quickly and
accurately.
Based on the electrical conductivity materials can be:
i. Conductors - are materials which allow electricity to flow through them, that is why, they
have free electrons. E.g. metals
ii. Insulators – are materials have no free electrons and they can’t conduct electricity.
E.g. plastic, wood, glass and rubber
That is why they are used to cover materials that carry electricity.
iii. Semiconductors - are materials having four valance electrons which have conductivity
between conductors and insulators. E.g. All group four elements or compounds such as gallium
arsenide or cadmium selenide.
5.1 Semiconductors
To increase the electrical conductivity of a semiconductor we use the following two methods.
A. Heating method
When we heat a semiconductor with high temperature, electrons surrounding the semiconductor
atoms can break away from their covalent bond and move freely within the material and if we
connected that heated semiconductor to a voltage source, these free electrons form current.
N.B: Semiconductors act as insulators at absolute zero temperature (zero kelvin).
B. Doping impurity atoms method
When impurity atoms from group three or group five are added to a pure [intrinsic]
semiconductor, its electrical conductivity can be increased, because adding impurity atoms into
a pure semiconductor is means of charge production. The process of adding impurity atoms to a
pure semiconductor is called doping. Doping intentionally introduces impurities into the intrinsic
semiconductor for the purpose of changing its electrical properties.
When impurity atom from group five such as antimony, arsenic, bismuth or phosphorus
is added to a pure semiconductor, it donates its free electrons to the semiconductor. In
this case the semiconductor becomes negative type and it is called N – type
semiconductor. Here, electrons are majority charge carries and protons are minority
charge carries. The impurity atom introduced to a pure semiconductor to gain N- type
semiconductor is donor impurity atom.
, On the other hand, if impurity atom such as aluminum, boron, gallium, or indium from
group three is added to a pure semiconductor the semiconductor needs one more electron
to complete its covalent bond. So, one of the covalent bonds is not completed. The
absence of an electron creates a hole. Here the holes are behaving like positive charge
carriers and this material is therefore called a P-type semiconductor. In this type of
semiconductor, the holes are majority and the electrons are minority. Here, holes are
majority charge carry. The impurity atom introduced to a pure semiconductor to gain P-
type semiconductor is receptor impurity atom.
Semiconductor can be:
i. Intrinsic [undoped or pure] semiconductor
It is semiconductor material, which has no impurity atom.
ii. Extrinsic [doped] semiconductor.
It is semiconductor material which has impurity atom.
N.B:
The main aim of doping is to make sure that there are either too many electrons (surplus)
or too few electrons (deficiency).
Holes and electrons are two types of charge carriers responsible for current in
semiconductor materials.
Exercise
1. Which of the following impurities could be used to convert intrinsic silicon to extrinsic P-type
silicon? A. Aluminum B. Germanium C. Arsenic D. zinc.
2. What type of impurities are chosen for doping to form N-type semiconductor?
A. trivalent B. tetravalent C. pentavalent D. both a and c
3. Electrons are the minority carriers in
A. extrinsic semiconductors B. P-type semiconductors C. intrinsic semiconductors D. N-type
semiconductors
5.2 P-N junction
When a P-type semiconductor is joined with the N-type semiconductor, a P-N junction is formed
and it is called diode.
A diode is a two-terminal electronic component that only conducts current in one
direction and blocks current in the reverse direction.
, When a P-N junction is formed, some of the electrons in the N-region diffuse across the junction
and combine with holes to form negative ions on the P-side. In so doing they leave behind
positive ions in the N-region.
The combination of electrons and holes near the junction creates a region called the depletion
region (layer). Within the depletion region, there are very few mobile electrons and holes. The
electric field created by the ions in the depletion region prevents any further diffusion across the
junction by establishing a barrier potential across the junction [i.e. depletion layer acts as like
insulator since the combined ions becomes stable atom]. The barrier potential of a P-N junction
depends on the type of semiconductor material. This is approximately 0.7V for silicon and 0.3V
for germanium. The symbol of a diode:
The arrow head points in the direction of conventional current flow. That means the anode is
connected to the P side and the cathode is connected to the N side.
Biasing of P-N junction diode
Applying a suitable DC voltage to a diode is known as biasing. It can be done in two ways:
forward biasing and reverse biasing.
A. Forward biased connection
It is a connection of the P-N junction diode with battery in which the positive terminal of
the battery is connected to the P-type semiconductor and the negative terminal to the N-
type semiconductor.
During forward biasing, because of the repulsive forces of the terminals of the battery, a few
number of free electrons and holes form stable bond and the depletion region becomes very thin
and narrow. This represents a low resistance path through the junction, allowing high currents to
flow.
B. Reverse biased connection
It is connection of the P-N junction diode with battery in which when the negative
terminal of the battery is connected to the P-type semiconductor and the positive terminal
to the N-type semiconductor.
During reverse biasing, because of the attractive forces of the terminals of the battery [when the
free electrons of the N-type and the holes of the P-type move away from the P-N junction], a
Basics of Electronics
Introduction
Electronic devices are devices that made from conductors and insulators and execute their
purpose electrically. Now a day, our daily lives are dependent on electronics. For example:
calculators, digital watches, mobile phones, televisions, and computers are just some of the
electronic devices that we use every day because, they simplify our activities. Electronics plays
an important role in different fields. For example, equipments in the aerospace industry, in the
automobile industries, in medicine [such as magnetic resonance imaging (MRI), computed
tomography (CT) and X-rays] rely on electronics in order to do their work quickly and
accurately.
Based on the electrical conductivity materials can be:
i. Conductors - are materials which allow electricity to flow through them, that is why, they
have free electrons. E.g. metals
ii. Insulators – are materials have no free electrons and they can’t conduct electricity.
E.g. plastic, wood, glass and rubber
That is why they are used to cover materials that carry electricity.
iii. Semiconductors - are materials having four valance electrons which have conductivity
between conductors and insulators. E.g. All group four elements or compounds such as gallium
arsenide or cadmium selenide.
5.1 Semiconductors
To increase the electrical conductivity of a semiconductor we use the following two methods.
A. Heating method
When we heat a semiconductor with high temperature, electrons surrounding the semiconductor
atoms can break away from their covalent bond and move freely within the material and if we
connected that heated semiconductor to a voltage source, these free electrons form current.
N.B: Semiconductors act as insulators at absolute zero temperature (zero kelvin).
B. Doping impurity atoms method
When impurity atoms from group three or group five are added to a pure [intrinsic]
semiconductor, its electrical conductivity can be increased, because adding impurity atoms into
a pure semiconductor is means of charge production. The process of adding impurity atoms to a
pure semiconductor is called doping. Doping intentionally introduces impurities into the intrinsic
semiconductor for the purpose of changing its electrical properties.
When impurity atom from group five such as antimony, arsenic, bismuth or phosphorus
is added to a pure semiconductor, it donates its free electrons to the semiconductor. In
this case the semiconductor becomes negative type and it is called N – type
semiconductor. Here, electrons are majority charge carries and protons are minority
charge carries. The impurity atom introduced to a pure semiconductor to gain N- type
semiconductor is donor impurity atom.
, On the other hand, if impurity atom such as aluminum, boron, gallium, or indium from
group three is added to a pure semiconductor the semiconductor needs one more electron
to complete its covalent bond. So, one of the covalent bonds is not completed. The
absence of an electron creates a hole. Here the holes are behaving like positive charge
carriers and this material is therefore called a P-type semiconductor. In this type of
semiconductor, the holes are majority and the electrons are minority. Here, holes are
majority charge carry. The impurity atom introduced to a pure semiconductor to gain P-
type semiconductor is receptor impurity atom.
Semiconductor can be:
i. Intrinsic [undoped or pure] semiconductor
It is semiconductor material, which has no impurity atom.
ii. Extrinsic [doped] semiconductor.
It is semiconductor material which has impurity atom.
N.B:
The main aim of doping is to make sure that there are either too many electrons (surplus)
or too few electrons (deficiency).
Holes and electrons are two types of charge carriers responsible for current in
semiconductor materials.
Exercise
1. Which of the following impurities could be used to convert intrinsic silicon to extrinsic P-type
silicon? A. Aluminum B. Germanium C. Arsenic D. zinc.
2. What type of impurities are chosen for doping to form N-type semiconductor?
A. trivalent B. tetravalent C. pentavalent D. both a and c
3. Electrons are the minority carriers in
A. extrinsic semiconductors B. P-type semiconductors C. intrinsic semiconductors D. N-type
semiconductors
5.2 P-N junction
When a P-type semiconductor is joined with the N-type semiconductor, a P-N junction is formed
and it is called diode.
A diode is a two-terminal electronic component that only conducts current in one
direction and blocks current in the reverse direction.
, When a P-N junction is formed, some of the electrons in the N-region diffuse across the junction
and combine with holes to form negative ions on the P-side. In so doing they leave behind
positive ions in the N-region.
The combination of electrons and holes near the junction creates a region called the depletion
region (layer). Within the depletion region, there are very few mobile electrons and holes. The
electric field created by the ions in the depletion region prevents any further diffusion across the
junction by establishing a barrier potential across the junction [i.e. depletion layer acts as like
insulator since the combined ions becomes stable atom]. The barrier potential of a P-N junction
depends on the type of semiconductor material. This is approximately 0.7V for silicon and 0.3V
for germanium. The symbol of a diode:
The arrow head points in the direction of conventional current flow. That means the anode is
connected to the P side and the cathode is connected to the N side.
Biasing of P-N junction diode
Applying a suitable DC voltage to a diode is known as biasing. It can be done in two ways:
forward biasing and reverse biasing.
A. Forward biased connection
It is a connection of the P-N junction diode with battery in which the positive terminal of
the battery is connected to the P-type semiconductor and the negative terminal to the N-
type semiconductor.
During forward biasing, because of the repulsive forces of the terminals of the battery, a few
number of free electrons and holes form stable bond and the depletion region becomes very thin
and narrow. This represents a low resistance path through the junction, allowing high currents to
flow.
B. Reverse biased connection
It is connection of the P-N junction diode with battery in which when the negative
terminal of the battery is connected to the P-type semiconductor and the positive terminal
to the N-type semiconductor.
During reverse biasing, because of the attractive forces of the terminals of the battery [when the
free electrons of the N-type and the holes of the P-type move away from the P-N junction], a
