2. Introduction to Electronics
Classification of Materials
Materials are classified into three groups
Conductors, Semi conductors and Insulators
Conductor
A material that easily conductors electrical current.
Copper Silver Aluminum
Conductors are characterized by with one valance electron very loosely bound
to the atom
Insulators
Those that does not conduct electrical current under normal conditions.
Most good insulators are compounds rather then single element material
having very high resistivity
3. Introduction to Electronics
What is electronics
The science of how to control electric energy
That energy in which electron have fundamental role
Electronics deal with electrical circuits that involve active electrical
components such as vacuum tubes transistors diodes and IC and associated
passive electrical component
Active components : Diode transistor and SCR
Passive Components: Resistors Capacitors and Inductors
4. Difference b/w active and passive components
Active components:
Those devices or components which require external source to their operation
is known as active components
For example Diode is an active component . So it is required an external
source to its operation
If we connect a diode in a circuit and connect the circuit to the supply
The diode will not conduct the current until the supply voltage reaches 0.3 in
case of Germanium or 0.7 in case of silicon
Active devices or components produce energy in the form of voltage or
current
5. Active and Passive Components
Passive component
Those devices or components which do not require external source to their
operation is called passive components
i.e., Resistors Capacitor inductors
Passive components
The passive components do not require external source to their operation
When a resistor is connect to the supply voltage it starts working
automatically without using a specific voltage
Passive device store or maintain energy in the form of voltage of current
6. Linear and Non Linear circuits
The non linear behavior of active components and their ability to control
electron flows makes amplification of weak signals possible
Electronics is widely used in information processing telecommunication and
signal processing
Linearity of circuit
A linear circuit in which circuit parameters ( resistance capacitance waveform
frequency are constant
In other words a circuit whose parameters are not changed with respect to
current and voltage
Non Linear circuits
Non linear circuit is an electric circuit whose parameters are varied with
respect to current and voltage
A circuit in which circuit parameters resistance inductance capacitance
waveform frequency is not constant is called non linear circuit
8. Material Used in Electronics
Semiconductors
A material that is between conductors and insulators in its ability to
conductor electrical current.
Semiconductor in its pure state is neither a good conductor nor a good
insulators.
Single element most commonly used semiconductors are Silicon and
Germanium.
Intrinsic and extrinsic semiconductors
Semiconductor in its pure form is known as intrinsic semiconductor
Intrinsic usually have poor conductivity because of equal number of positive
and negative carriers
Semiconductors in impure form is called extrinsic semiconductor,
they are relatively good conductors as compared to intrinsic semiconductors.
To form an extrinsic semiconductors, the intrinsic conductor is added with
impurities ( negative or positive charge carriers )
The process of adding impurities to an intrinsic semiconductor is known as
doping process.
9. Introduction to Electronics
Energy Gap or Band Gap
The valence shell of an atom represents a band of energy level
When electron acquires enough additional energy it can leave the valence
shell become a free electron known as conduction band
The difference in energy between the valence band and the conduction band
is called energy gap or band gap
This is the amount of energy that a valence electron must have in order to
jump from the valance to conduction band
11. Introduction to Electronics
Silicon and Germanium
The atomic structure of silicon and Germanium are compared in figure
Silicon is used in diode transistors and IC’s and other semiconductor devices
Both silicon and germanium have the characteristics four electrons
12. Introduction to Electronics
The valence electrons in Gr are in 4th Shell while those in Si are in 3rd shell.
Si is closed to the nucleus
This means that Gr valence electrons are at higher energy level than those in
Si
Therefore Gr requires a smaller amount of additional energy to escape from
atom,
However this property makes Gr more unstable at higher temperature and
results in excessive reverse current
This is why silicon is more widely used semiconductor material
13. Introduction to Electronics
The electrons of an atom can exist only within
prescribed energy bands
Each shall surround the nucleus corresponds to
a certain energy band and is separated from
adjacent shell by band gaps in which no
electron can exist
Figure shows the energy band diagram for an
unexcited atom in a pure silicon crystal
This is done with no external energy such as
heat
14. Conduction Electrons and Holes
An Intrinsic (Pure) silicon at room temp has sufficient heat energy for some
valence electrons to jump the gap from valance to the conduction band
becoming free electrons
Free electrons are also called conduction electrons
A vacancy is left in the valance band within the Si crystal.
This vacancy is known as hole
For every electron raised to the conduction band by external energy there is
one hole left in the valance band
Creating what is called an electron hole pair
Recombination occurs when a conduction band electron loses energy and falls
back into a hole in the valance band
15. Introduction to Electronics
When a voltage is applied across a piece of intrinsic silicon
Thermally generated free electrons in the conduction band are free to move
randomly in the crystal structure are now easily attached towards the positive
end
This movement of free electrons is one type of current in a semi conductor
material known as electron current
16. Introduction to Electronics
The second type of current occurs in the valance band
The holes created by the free electrons exist
Electrons remaining in the valance band are still attached to their atoms and
are not free to move randomly in the crystal structure as are the free
electrons
However a valance electron can move into a nearby hole with little change in
its energy level thus leaving another hole where it come from
The hoe has moved from one place to another in the crystal structure
Thus the current valance band is produced by valance electrons is is called
hole current
17. N-Type and P-Type Semiconductors
Semi conductive material do not conduct current well and are of limited value in their
intrinsic state
As we know semiconductors are generally poor conductors
This is because of limited number of free electrons in the conduction band and holes in
the valance band
Intrinsic silicon must be modified by increasing the number of free electrons or holes to
increase its conductivity and make it useful
This conductivity can be drastically increased by the controlled addition of impurities
to the pure semi conductive material.
The two categories of impurities are n-type and p-type
18. N-Type and P-Type Semiconductors
N-Type Semiconductor
To increase the number of conduction band electrons in intrinsic silicon,
A Pentavalent impurity atom are added
There are atoms with five valance electrons such as Arsanic Bismuth and antimony (Sb)
Each pentavalent atom (antimony ) forms a covalent bonds with four adjacent silicon
atoms leaving one extra electron
This extra electron becomes a conduction electron because it is not involved in bonding
called as donor atom
A conduction electron created by this doping process does not leave a hole in the
valance band because it is in excess of the number required to fill the valance band
19. N-Type and P-Type Semiconductors
Majority and Minority Carriers
Most of the current carriers are electrons
Silicon doped with pentavalent atoms is an n-
type semiconductor
The “n” stand for negative charge on an electron
In this case the electrons are called the majority
carriers
Holes in an n type material are called minority
carriers
20. N-Type and P-Type Semiconductors
To increase the number of holes in intrinsic silicon
Trivalent impurity atoms are added
These atoms with three valance electrons such as boron (B)
Each trivalent atom forms a covalent bond with four adjacent silicon atoms
All three of the boron atoms valance electrons are used in the covalent bond
with four adjacent silicon atoms
And since four electrons are required
A hole results when each trivalent atom is added
The number of holes can be carefully controlled by the number of trivalent
impurity atoms added to the silicon
21. N-Type and P-Type Semiconductors
Majority and Minority carriers
Silicon doped with trivalent atoms is
called a P-type semiconductor
The holes are the majority carriers in p-
type material
Conduction band electrons in p-type
material are the minority carriers
22. PN junction
PN junction
When a silicon block is doped with a trivalent impurity and the other part
with a pentavalent impurity
A boundary called the PN junction is formed between the resulting p-type and
n-type portion
The N-type and P-type semiconductors forms a boundary between the two
regions and a diode is created
The P region has many majority carriers “holes” from the impurity and only
few thermally generated free electrons
The N region has many free electrons from the impurity atom and only a few
thermally generated holes
A diode is made from a small piece of semiconductor material usually silicon
in which half is doped as a p region and half is doped as n region
24. PN junction
The free electrons in the n region are randomly drifting in all directions
At the instant of the PN junction formation
The free electrons near the junction in the n region begin to diffuse across
the junction into the p region, combine with holes near the junction
When a pn junction is formed the n region loses electrons as they diffuse
across the junction
This creates a layer of positive charges near the junction
The p region loses holes as the electrons and holes combine
This create a layer of negative charges near the junction
The two layers of positive and negative layer form a depletion region
