1new Introduction.ppt

Course: Basic Electronics
1
7 November 2023
Topic – P-N Junction Diode
Dr. Sharad T. Jadhav
Associate Professor
ECE Department
SITCOE, Yadrav

Syllabus
UNIT – I : DIODES AND CIRCUITS
PN junction diode,
V-I characteristics,
Diode as a rectifier,
Specification of rectifier diodes,
HW, FW, Bridge rectifiers,
Equation for Idc, Vdc, Vrms, Irms, efficiency and
ripple factor for each configuration,
Capacitor filter, ripple factor,
Zener diode characteristics, specification, zener
voltage regulator,
LED characteristics, configurations – discrete,
seven
segment, Bar graph, matrix, concept of multiple
display.
7 November 2023 UNIT - I Diodes and Circuits 2

Atomic Structure
All matters is made up of atoms; and all atoms
consist of electrons, protons, and neutrons.
In this section we will learn about the structure of
the atom, electron orbits and shells, valence
electrons, ions, and semiconductor materials –
Silicon and Germanium

Atomic Structure
After completing this section, you should be able to:
 Discuss the basic structure of atom.
 Define nucleus, protons, neutrons, and electron
 Describe an element’s atomic number
 Explain electron shells
 Explain what a valence electron is
 Describe ionization
 Explain what a free electron is

Any substance, solid, liquid or gaseous is made
up of molecules and molecules are made up of
atoms.
Atoms contains tiny particles called protons,
electrons and neutrons. Which are called as
fundamental particles.
Protons are positively charged, electrons are
negatively charged and the neutrons are
electrically neutral
The structure of an Atom

FIGURE 1-1 The Bohr model of an atom showing electrons in orbits and around
the nucleus, which consists of protons and neutrons. The “tails” on the electrons
indicate motion.
Thomas L. Floyd
Electronic Devices, 6e and Electronic
Devices: Electron Flow Version, 4e

FIGURE 1-2 The two simplest atoms, hydrogen and helium.

+
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1. The Nucleus: The nucleus of an atom consists
of two types particles – protons and neutrons.
For a given atom, the number of protons in the
nucleus is normally equals to the number of
orbiting electrons
+
-
-
-
-
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Nucleus

2. Atoms are electrically neutral: Since the protons and
orbital electrons are equal in number, their equal and
opposite charge will neutralize each other electrically.
Therefore atoms are normally electrically neutral.
An electron has a negative charge equal to 1.6 X 10 -19
coulomb and a neutron has no charge at all.
The mass of an electron is 9.1 X 10-31 Kg
+
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Nucleus

+
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Nucleus
3. Atoms can be converted into ions:
If an atom losses an electron then the number of
protons becomes higher than the number of
electrons. Therefore the atom becomes
positively charged and it is referred to as a
positive ion.

+
-
-
-
-
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Nucleus
3. Atoms can be converted into ions:
Similarly if an atom gains an additional electron
then it becomes negatively charged and called
as negative ion.

4. Electron orbits or shell:
Electrons can occupy only certain orbital rings or shells which are
at a fixed distance from the nucleus.
Each shell can contain only a particular number of electrons.
In general a shell can contain at the most 2n2 number of
electrons where “n” is the shell number.
The exception for this rule is that the outermost shell cannot
contain more than eight electrons.
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-
- -
-
-
- -
-
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Nucleus
Electrons
Outermost orbit
Valence electrons

5. Valence shell and valence electrons:
The outermost shell is known as the valence shell and the
electrons in it are called as valence electrons.
These valence electrons determine the electrical characteristics
of each particular atom.
The valence shell may be completely filled or partially filled of
valence electrons.
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Nucleus
Electrons
Outermost orbit
Valence electrons

Introduction to semiconductor
The materials such as copper, aluminium etc. are good
conductors of electricity.
While the materials such as wood , glass, mica etc. are
bad conductors of electricity and are called insulators.
There is another class of materials, whose conductivity
i.e. ability to carry electricity, lies between that of
conductors and insulators. Such materials are called
semiconductors.
Germanium (Ge) and Silicon (Si) are two well known
semiconductor.

The structure of Silicon (Si) Atom
Silicon Atom
A silicon atom consists of 14 protons and 14 neutrons inside the
nucleus and 14 revolving electrons.
These 14 electrons are distributed among different shell.
+14
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- -
-
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- -
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Nucleus
Electrons
Outermost orbit
Valence electrons

Silicon Atom
The first shell contains 2 electrons ( 2n2 = 2 since n=1 first shell)
+14
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2

Silicon Atom
The second shell contains 8 electrons ( 2n2 = 8 since n=2 second shell)
+14
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- -
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- 2
8

Silicon Atom
While third shell which is called as valence shell contains 4 electrons
+14
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Nucleus
Electrons
Outermost orbit
Valence electrons
2
8
4

The structure of Germanium (Ge) Atom
Germanium Atom
+32
-
- Nucleus
2

Germanium Atom
-
Nucleus
2
+32
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- -
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8

Germanium Atom
The third shell contains 18 electrons ( 2n2 = 18 since n=3 third shell)
+32
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Nucleus
Electrons
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2
8
18

Germanium Atom
The third shell contains 18 electrons ( 2n2 = 18 since n=3 third shell)
And the outermost shell contains 4 valence electrons.
+32
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Nucleus
Electrons
Outermost orbit
Valence electrons
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2
8
18
4

Silicon as well as Germanium atoms contains 4 electrons in the valence
shell.
If there are 4 electrons in the outermost orbit the semiconductor material is
called as Tetravalent semiconductor or pure or Intrinsic semiconductor

Ionization

Ionization
When in equilibrium, an atom is electrically neutral, as
the number of protons is exactly equal to the number of
electrons.

Ionization
electrons.
But if the electrons from the outermost orbit (valence
electron) is extracted, then the atom does not remain
electrically neutral.

Ionization
electrons.
Since it has lost one electron, it has lost some negative
charge. So the atom becomes positively charged and
called as positive ion.

Ionization
electrons.
On the other hand, addition of an electron to an atom will
convert it into negative ion.

Ionization
electrons.
On the other hand, addition of an electron to an atom will
convert it into negative ion.
The process of conversion from an electrically neutral to
an ion is called as Ionization.

Concept of energy levels
Each electronic orbit has an energy level associate with it.
The electrons in the inner orbits are more closely bound to the
nucleus and posses less energy.
As we move towards the valence shell, the binding force between
nucleus and electrons reduces and the electrons posses higher
energy.
+
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-
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- -
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-
Energy levels increases as
we away from the nucleus
Valence orbit shell
has highest energy level
Shell 1
Lowest energy
nucleus

Free electrons
The valence electrons are very loosely bound with the nucleus .
If an external energy is given to them, they can easily break away
from the nucleus and become free.
Such electron which are free from the force of attraction of nucleus
are called as free electrons
+
- - -
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-
-
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- -
-
-
Valence orbit shell
Shell 1
Lowest energy
nucleus - Free electron

Free electrons
These free electrons posses an energy which is higher than that of
valence electrons.
The electric current flows due to these free electrons and they are
said to be in the conduction band.
The energy level of conduction band is higher than that of valence
shell
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-
Valence orbit shell
Shell 1
Lowest energy

Energy Bands
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-
Valence orbit shell
1st Band
1st Band
2nd Band
Valence band
Conduction band
2nd Band
Valence band
Edge of the nucleus
1st Band
2nd Band
Valence Band
conduction
Band
Energy
Forbidden energy gap
EG

Energy Bands
1st Band
2nd Band
Valence band
Conduction band
Edge of the nucleus
1st Band
2nd Band
Valence Band
conduction
Band
Energy
•The electrons in the first shell will require the highest amount of energy
for their extraction. Therefore the first shell is said to have lowest
amount of energy associate with it
On the other hand, the valence electrons require the lowest amount of
energy for their extraction. Hence valence shells are said to have the
highest amount of energy.

Energy Bands
1st Band
2nd Band
Valence band
Conduction band
Edge of the nucleus
1st Band
2nd Band
Valence Band
conduction
Band
Energy
EG
•Valence Band :
the valence band corresponds to the valence electrons present
in the different atoms of the materials.
Energy associates with the valence band is the second highest
as shown in figure

Energy Bands
1st Band
2nd Band
Valence band
Conduction band
Edge of the nucleus
1st Band
2nd Band
Valence Band
conduction
Band
Energy
EG
•Conduction Band :
Conduction band has the highest energy associated with it
The electrons in the conduction band are the free electrons i.e. the
electrons which are disconnected from their respective atoms.
Conduction band electrons are actually responsible for the flow of
current . More number of electrons in the conduction band more
will be the current

Energy Bands
1st Band
2nd Band
Valence band
Conduction band
Edge of the nucleus
1st Band
2nd Band
Valence Band
conduction
Band
Energy
EG
• Forbidden Gap :
As shown in figure the forbidden gap is the energy gap that
separates the conduction and valence band.
No electrons can normally exist in the forbidden gap. For any given
type of material the forbidden gap may be large, small or even
nonexistent.
The materials are classified as conductors, insulators and
semiconductors based on the relative width of the forbidden gap.

Jump from valence band to conduction band
If the valence band electrons can jump across the
forbidden gap and enter into the conduction band then
they will become free electrons and be available for
conduction.
The valence electrons can jump if we provide additional
energy to them . This additional energy can be supplied
by increasing the temperature or focusing light on the
material etc.
This is the reason why conductivity of certain materials
increase with increase in temperature.

Let us understand conductor, insulators and
semiconductors based on their energy band diagram
Conductors
Conductors are materials which allows the current to flow very
easily. This is due to the large number of free electrons present in
the conductors.
From the energy band diagram of conductors shown in figure, for
metals like copper, aluminium etc. there is no “forbidden gap”
present between the valence and conduction band.
Therefore even at room temperature, a large number of free
electrons are present and available for conduction.
Conduction
Band
Valence
Band
Bands
overlap
Conduction band
Valence band

Insulators
The energy band diagram of an insulator is shown in figure
The forbidden gap between the conduction band valence band is
extremely wide.
Normally the valence electrons cannot jump that far and enter into
the conduction band. Therefore conduction those not takes place
and these materials are known as insulators
Conduction
Band
Valence
Band
Large
forbidden
gap
Conduction band
Valence band
EG = 6 eV

Semiconductors
Semiconductor have the conduction properties which are in between
those of conductors and insulators.
We can say that semiconductors are neither conductors nor
insulators. Forbidden gap is very narrow as compared to that of the
insulator.
The forbidden gap for Silicon EG = 1.1 eV
For Germanium EG = 0.72 eV
Conduction
Band
Valence
Band
small
forbidden
gap
Conduction band
Valence band
EG = 1 eV

Conduction
Band
Valence
Band
small
forbidden
gap
EG = 1 eV
Conduction
Band
Valence
Band
Large
forbidden
gap
Conduction
Band
Valence
Band
Bands
overlap
Conductor Insulator Semiconductor

Why silicon is more widely used semiconductor material
The valence electrons in germanium are in the fourth shell
while those in silicon are in the third shell, i.e. closer to the
nucleus.
This means that the germanium valence electrons are at
higher energy levels than those in Silicon.
Hence germanium valence electrons will need smaller amount
of additional energy to escape from the atom.
Due to this, the germanium produces more number electron
hole pairs than silicon.
Hence the leakage current is more in germanium than that of
silicon.
This property make germanium more unstable at high
temperatures, therefore silicon is more widely used material
than germanium.

Types of Semiconductors
The semiconductors are classified into two categories as:
Intrinsic semiconductors and
Extrinsic semiconductors.

Intrinsic Semiconductors
Intrinsic means pure, so intrinsic semiconductors are the
semiconductors in their purest possible form.
The presence of impurity (i.e. atoms of other material) is as
low as 1 part in 100 million parts of the semiconductor atoms.
The intrinsic semiconductors are insulators or very very poor
conductors, at room temperature.
Silicon and germanium are intrinsic semiconductor

Extrinsic Semiconductors
Extrinsic means impure, so we can obtain the extrinsic
semiconductors from intrinsic ones by adding impurities to
them.
Impurity is nothing but some other material. The process of
adding impurities is called as “ doping”
Due to doping, the conductivity of the semiconductor
increases.
Extrinsic semiconductor are of two types:
n- type semiconductor
p- type semiconductor
The type of extrinsic semiconductor (n or p) depends on the
type of impurity ( or dopant ) being used

two dimensional representation
We know that in a silicon or germanium atom there are four
valence electrons
Si

Si
Thomas L. Floyd

We know that in a silicon or germanium atom there are four
valence electrons
In an intrinsic Si or Ge crystal these four valence electrons are
bound to four adjacent atoms
Si
Si Si
Si
Si
Si
Si
Si
Si
Covalent Bond

Each one of the four valence electrons in each atoms forms a
bond with a valence electrons from the adjoining atom as
shown. This bond is nothing but sharing of electrons. These
bonds are Known as covalent bond
Si
Si Si
Si
Si
Si
Si
Si
Si
Covalent Bond

Si Si
Si
Si
Si
Si
Covalent Bond
Thomas L. Floyd

Conduction in intrinsic semiconductor
The intrinsic semiconductor behaves like perfect
insulator at the absolute zero temperature.
But the behavior changes with increase in
temperature. At around the room temperature,
electrons becomes available for conduction and
current can flow.

Conduction in intrinsic semiconductor
The intrinsic semiconductor behaves like perfect
insulator at the absolute zero temperature.
But the behavior changes with increase in
temperature. At around the room temperature,
electrons becomes available for conduction and
current can flow.
FIGURE Creation of electron-hole pairs in a silicon crystal. Electrons in the conduction band
are free.
Thomas L. Floyd

FIGURE Electron-hole pairs in a silicon crystal. Free electrons are being generated
continuously while some recombine with holes.
Thomas L. Floyd

Generation of electron-hole pairs at
increased temperature
At increase in temperature many valence electrons will absorb
the thermal energy, breaks the covalent bonds and go into the
conduction band
Thus they becomes free for conduction. When an electron
break a covalent bond and becomes free, a vacancy is
created in the broken covalent bond.
Si Si
Si Si
Free electron
hole

This vacancy is called as “hole”. Thus corresponding to every
free electron, hole is created.
Therefore the number of free electrons are generated due to
increased in temperature is exactly equal to the number of
holes.
As the free electrons and holes are generated in pairs they
are called as thermally generated electron hole pair.
Si Si
Si Si
Free electron
hole

The electrons and holes both can operate as charge carriers.
The holes is said to have a positive charge as it is nothing but
absence of an electron.
Thus the conductivity of an intrinsic semiconductor thus
increases due to the increase in temperature.
Si Si
Si Si
Free electron
hole

Recombination
The free electrons in the conduction band, when come across
the hole will jump into the hole.
This process is called as the recombination process
Si Si
Si Si
Free electron
hole

Recombination
When a conduction band electron return back to valence
band, and recombines with a hole, it release energy equal to
the energy gap between conduction and valence bands.
This principle is used in the light emitting diode (LED)
Si Si
Si Si
Free electron
hole

FIGURE Hole current in intrinsic silicon.
Thomas L. Floyd

Electron and hole current
Electron Current
As we apply voltage across a piece of intrinsic semiconductor
material, the thermally generated free electrons in the
conduction band are attracted towards the positive end
The current is constitute due to the movement of free
electrons is called as electron current as shown in figure
Si Si
Si

Hole Current
Si Si
Si

Hole Current
Si Si
Si
Si Si
Si

Hole Current
Si Si
Si
Si Si
Si
Hole movement electron movement

Total current
The flow of an electric current is due to the movement of
electrons in the conduction band and movement of holes in
the valence band.
Total current = electron current + hole current
Si Si
Si

FIGURE Electron current in intrinsic silicon is produced by the movement of thermally
generated free electrons.
Thomas L. Floyd

Semiconductors have a negative
temperature coefficient of resistivity
As the temperature rises, more number of electrons will
absorb the thermal energy to break the covalent bonds and
contributes to the number of free carriers.
The increase in the number of electrons and holes will
increase the conductivity of the semiconductor and results in
the lower resistance level.
Thus the resistance of the semiconductor decreases with
increase in temperature. Therefore they are said to have a
“ negative temperature coefficient” of resistivity.

Conventional current
The current flow from positive to negative is referred to as
conventional current.
Under the influence of the external dc source or battery the free
electrons in the semiconductor slab which are negatively charged
will attracted towards the positive terminal and holes being
positively charged will be attracted towards the negative terminal of
the external battery.
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-
-
h
h
h
e
e
e
Electron flow
External DC source
Semiconductor slab

Extrinsic Semiconductors
Doping Process
In the process of doping, impurities are added to the
pure Silicon or Germanium.
The impurities are the material used to dope the intrinsic
semiconductor materials. These materials can be of two
types:
1. Donor impurity 2. Acceptor impurity

Donor impurity
The material which is being used as impurity in the
process of doping is called as “dopant”.
When the dopant is Pentavalent atom i.e. the atom
containing five valence electrons then it is called as the
“ donor impurity” and the doping is called as “ donor
doping”
Donor doping is used to manufacture n-type extrinsic
semiconductor.

Acceptor impurity
When the dopant is trivalent atom i.e. the atom
consisting of only three valence electrons, then it is
called as the “ acceptor impurity” and the doping is called
“acceptor doping”.
Acceptor doping is used to manufacture p-type extrinsic
semiconductor.

n-type semiconductor
The n–type semiconductor is formed by adding small
amount of Pentavalent impurity to the pure Si or Ge
material which act as base material.
The Pentavalent atom is the one which has five valence
electrons.
The examples of Pentavalent materials are :
Antimony (Sb)(51),
Arsenic (As) (33) and
Phosphorous (P)(15).

n-type semiconductor
formation of covalent bond
As
Si Si
Si
Si
Si
Si
Si
Si
Covalent Bond
Fifth valence electron
Of Arsenic
(Extra Free electron)
When a pentavalent impurity such as Arsenic is added to the
intrinsic semiconductor, four valence electrons of Arsenic
atom form four covalent bonds with four valence electrons of
the neighboring silicon atom

FIGURE Pentavalent impurity atom in a silicon crystal structure. An antimony (Sb) impurity
atom is shown in the center. The extra electron from the Sb atom becomes a free electron.
Thomas L. Floyd

majority and minority carriers in the n-type semiconductor
A large number of free electrons are present along with a small number of
thermally generated holes in an n-type semiconductor.
So the conduction largely takes place due to the free electrons. Therefore
the free electrons are called “ majority carrier” and holes are known as
“ minority carrier”.
When an external DC voltage is applied to the n-type semiconductor
material, the free electrons move towards the positive terminal of the
source and hole move towards the negative end
-
-
h
h
e
e
Electron flow
N-type material
-
-
-
e
e
e
-
-
e
e
-
e -
e
- e
-
e
-
e
- e

P-type semiconductor
The P–type semiconductor is formed by adding small
amount of trivalent impurity to the pure Si or Ge material
which act as base material.
The trivalent atom is the one which has three valence
electrons.
The examples of trivalent materials are :
Boron(B)(5),
Gallium(Ga)(31) and
Indium(In)(49).

p-type semiconductor
formation of covalent bond
Ga
Si Si
Si
Si
Si
Si
Si
Si
Broken Covalent Bond
Hole created due to
Incomplete bond
When a trivalent impurity such as Gallium is added to the
intrinsic semiconductor, three valence electrons of gallium
atom form three covalent bonds with three valence electrons
of the neighboring silicon atom
Covalent Bond

FIGURE 1-16 Trivalent impurity atom in a silicon crystal structure. A boron (B) impurity atom
is shown in the center.
Thomas L. Floyd

majority and minority carriers in the p-type semiconductor
+
+
h
h
Electron flow
P-type material
-
-
e
e
+
+
+ +
+
+
+
+ +

p-n junction
P-type semiconductor and an n-type semiconductor are
joined together with the help of special fabrication
technique to form a p-n junction
+
+
+ +
+
+ +
+
-
-
-
-
-
-
-
-
p-type
semiconductor
n-type
semiconductor

p-n junction
P-type semiconductor and an n-type semiconductor are
joined together with the help of special fabrication
technique to form a p-n junction
+
+
+ +
+
+ +
+
-
-
-
-
-
-
-
-
P-type
semiconductor
n-type
semiconductor
junction

p-n junction
Terminals are brought out for the external connection
with p-type semiconductor. The p-side is called as anode
and the n-side is called as cathode.
Anode Cathode
+
+
+ +
+
+ +
+
-
-
-
-
-
-
-
-
P-type
semiconductor
n-type
semiconductor
junction

p-n junction
Terminals are brought out for the external connection with p-
type semiconductor. The p-side is called as anode and the
n-side is called as cathode.
The p-n junction forms the basic semiconductor device called
diode
Anode cathode
+
+
+ +
+
+ +
+
-
-
-
-
-
-
-
-
P-type
semiconductor
n-type
semiconductor
junction

Diffusion
At the junction, one side has a high concentration of
holes and other side has high concentration of electrons.
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode

Diffusion
At the junction, one side has a high concentration of
holes and other side has high concentration of electrons.
Due to this a concentration gradient is created across
the junction, and a process of charge carrier as shown in
figure.
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode

formation of the depletion region
Note that no external voltage is applied between the
terminals of the p-n junction, hence the p-n junction is
said to be unbiased.
+
+
+ +
+
-
-
-
-
-
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode
+
-

The free electrons from “n” side will diffuse into the p
side and recombine with the holes present there.
+
+
+ +
+
-
-
-
-
-
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode
+
-

Each electron diffusing into the “p” side will leave behind
a positive immobile ion on the n-side.
When electron combine with a hole on the p-side, an
atom which accepts this electron, losses its electrically
neutral status and become a negative immobile ion as
shown in figure
+
+
+ +
+
-
-
-
-
-
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode
+
-

+
-
n-type
semiconductor
junction
Anode cathode

+
+
+ +
+
-
-
-
-
-
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode
+
-
+
+
+
-
-
-

+
+
+ +
+
-
-
-
-
-
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode
+
-
+
+
+
-
-
-
shown in figure

+
+
+ +
+
-
-
-
-
-
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode
+
-
+
+
+
-
-
-
Negative immobile ions Positive immobile ions
shown in figure

Due to this recombination process, a large number of
positive ions accumulate near the junction on the n-side
and a large number of negative immobile ions will
accumulate on the p-side near the junction
+
+
+
-
-
-
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode
-
-
-
+
+
+
Depletion
region

The negatively charged ions on the p-side will start
repelling the electrons which attempts to diffuse into the
p-side and after some time the diffusion will stop
completely.
At this point the junction is said to have attained an
equilibrium.
+
+
+
-
-
-
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode
-
-
-
+
+
+
Depletion
region

width of the depletion region
Practically the width of depletion region is very small of
the order of 0.5 to 1 micron where 1 micron is equal to
1X10-6 meter.
Thus the depletion region is very thin as compared to the
width of p and n region.
+
+
+
-
-
-
P-type
semiconductor
n-type
semiconductor
junction
Anode cathode
-
-
-
+
+
+
Depletion
region

Barrier potential or junction potential
Due to the presence of immobile positive and negative ions on
opposite sides of the junction, an electric field is created across
the junction. This electric field is known as the “barrier
potential”.
The polarities of barrier potential are decided by the type of
immobile ions present on the two sides of the junction.
+
+
+
-
-
-
P-type
semiconductor
n-type
semiconductor
Anode cathode
-
-
-
+
+
+
Depletion
region
- + Barrier potential or
Junction potential

Barrier potential or junction potential
Barrier potential is measured in volts. The barrier potential for
silicon is about 0.6 Volt whereas its value for the Germanium
is 0.2 Volt.
+
+
+
-
-
-
P-type
semiconductor
n-type
semiconductor
Anode cathode
-
-
-
+
+
+
Depletion
region
- + Barrier potential or
Junction potential

penetration of depletion region
The penetration of the depletion region into p or n-side
depends on the doping levels of those sides
If both these sides are equally doped then the depletion
region penetrates equally on both the sides as shown in
figure:
P N
J
Equal penetration
On both side
Both sides are equally doped

But if p-region is lightly doped as compared to the n-
region the penetration of depletion region is more on the
p-side as shown in figure
P N
J
More penetration
On p-side
P-side is lightly doped

Similarly if n-side is lightly doped as compared to p-side
then the depletion extend more into the n-side as sown
P N
J
More penetration
On n-side
n-side is lightly doped

P N
J
Equal penetration
On both side
Both sides are equally doped
More penetration
On p-side
P-side is lightly doped
P N
J
P N
J
More penetration
On n-side
n-side is lightly doped
Thus the depletion region always penetrates more on the side which is lightly doped
as compared to the other

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