INTRODUCTION TO
SEMICONDUCTOR
MATERIALS AND DEVICES
Presented By
S.ARUNBHAARAT
6017f17de69b11e9b0fe59835bdf11f2(App
SASTRA Deemed To be University
B.Tech ECE
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ACKNOWLEDGEMENT
In preparation of my assignment, I had to take the help and guidance
of some respected persons. As the completion of this assignment
gave me much pleasure, I would like to show my gratitude DR.AJAY
SEMALTY, Course Instructor, from ACADEMIC WRITING under UGC
SWAYAM ONLINE COURSE for giving me a good guidelines for
assignment throughout numerous consultations. I would also like to
expand my gratitude to all those who have directly and indirectly
guided me in writing this assignment.
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DISCOVERY
Vacuum Tubes- First Generation
Contained Heavy Coverage of tubes in Solid state Era.
Many Engineers joined together and discovered First Transistor on
1950
Miniaturisation limited by three factors
1.Quality
2. Network design
3. Manufacturing Equipment.
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WHY SEMICONDUCTOR
SELECTED??
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WHY SEMICONDUCTOR
SELECTED??
Semiconductors have a unique atomic structure that allows their conductivity to be controlled by
stimulation with electric currents, electromagnetic fields, or even light.
Therefore ,Semiconductors and semiconductor devices are the building blocks of all the electronic
devices.
Semiconductor materials generally have conductivity between metals and insulators.
Types of semiconductors
(i) Elemental semiconductors: Si and Ge
(ii) Compound semiconductors :
 Inorganic: CdS, GaAs, CdSe, InP, etc.
 Organic: Anthracene, doped pthalocyanines, etc.
 Organic polymers: Polypyrrole, polyaniline,
polythiophene, etc.
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BAND THEORY
Isolated atoms of materials have well defined energy levels over which
electrons are distributed (in different orbits)
In crystalline form, when the atoms are closely spaced their outer energy
levels join together to form two separate bands called Valance band and
Conduction band
The energy gap between the valance band and the conduction band is
known as Forbidden energy gap( Eg) or Energy band gap or simply Energy
gap
The conductivity of materials depends on this energy gap. 6

ENERGY BAND STRUCTURE
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ENERGY BAND STRUCTURE
Metals SemiconductorNon-Metals
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INTRINSIC SEMICONDUCTORS
An intrinsic semiconductor behaves like an insulator at T = 0 K
It is the thermal energy at higher temperatures (T > 0K), which excites some
electrons from the valence band to the conduction band
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EXTRINSIC SEMICONDUCTOR
To improve the conductivity the pure Semiconductors are added with small
amounts of Trivalent (Gallium, indium) or Pentavalent (Arsenic, Phosphorous)
impurities
Doping:
Adding small amounts of trivalent or pentavalent impurities to pure
semiconductors to improve their conductivity is known as doping
The Two types of extrinsic semiconductors are:
n-Type semiconductor &
p-Type semiconductor
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N-TYPE SEMICONDUCTOR
Pure semiconductors doped with small amounts of pentavalent impurities
are known as n-type semiconductors
The four valance electrons of each impurity atom form covalent bond with
the neighboring semiconductor atoms.
The fifth unpaired electron will remain at an energy level much higher than
the bound electrons
This energy level is known as the donor energy level
The donor energy level is very close to conduction band( 0.01 to 0.05 eV).
This electrons can easily jump in to conduction band to become free
electrons by absorbing thermal energy
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N-TYPE SEMICONDUCTOR
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P-TYPE SEMICONDUCTORS
In this case the three valance electrons of each trivalent impurity atom forms
covalent bonds with the neighboring semiconductor atom
the fourth neighboring atom will have an unoccupied energy state.
This energy state is called acceptor energy level
Accepter energy level is very close to valance band ( 0.01 to 0.05 ev)
Electrons from valance band can easily jump in to Acceptor energy level
This creates Holes in the valance band
the number holes the valance band is greater than the free electrons in the
conduction band. nh > ne
Majority current carriers in p-type semiconductors are holes
Again ne x nh = ni
2
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P-TYPE SEMICONDUCTOR
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P-N JUNCTION (SEMICONDUCTOR
DIODE)
p-n junction is the basic building block of many semiconductor devices like
diodes, transistor, etc
P-type & n-Type semiconductors are fused together to make p-n Junction or
Diode
(a). Diffusion and Drift
In n-type- semiconductor concentration of electrons (number of electrons
per unit volume) is more than the concentration of holes
In a p-type semiconductor, concentration of holes is more than the
concentration of free electrons
During the formation of p-n junction holes diffuse from p-side to n-side (p
→ n) and electrons diffuse from n-side to p-side (n → p)
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P-N JUNCTION (SEMICONDUCTOR
DIODE)
This motion of charge carries gives rise to diffusion current across the
junction
Due to this diffusion of current carriers, a layer of negative charge (negative
space-charge region) on the p-side and a layer of positive charge (or
positive space-charge region) on n-side of the junction are developed.
This region at the junction free of current carriers is known as Depletion
layer
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P-N JUNCTION (SEMICONDUCTOR
DIODE)
This diffusion of majority current leads to a layer of +ve charge on n side
and –ve charge on p side
This charge accumulation on either side near the junction produces an
electric field with in the depletion layer from n side to p side, known as
Barrier electric field (Eb)
Due to this electric field electrons move from p side to n side and holes from
n side to p side
This motion of charges due to barrier electric field is known as Drift
That is drift current is opposite to diffusion current
At equilibrium state,
drift current = diffusion current.
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P-N JUNCTION (SEMICONDUCTOR
DIODE)
Due to the barrier, electric field n side will be at a higher potential compared
to the p side. This potential difference across the depletion layer is called
barrier potential ( V0)
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P-N JUNCTION DIODE UNDER FORWARD
BIAS
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P-N JUNCTION DIODE UNDER
FORWARD BIAS
P side is connected to positive & n side is connected to negative
External potential V appears across the depletion layer
Due to the affect of external potential free electrons and holes accumulate in
the depletion layer
Thickness of depletion layer decreases
Free electrons diffuse towards the positive end and holes diffuse to the
negative end setting up a diffusion current( of the range of a few mA)
The current through the diode remains small at the beginning
As external voltage increases, at a particular voltage the current starts
increase rapidly
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P-N JUNCTION ( DIODE)
FORWARD BIAS
His voltage is known as Thresh hold voltage or Cut in Voltage ( 0.2 V for Ge
& 0.7 Volt for Si).
Beyond thresh hold voltage the diode acts as a good conductor and V-I
relationship is more or less linear
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REVERSE BIAS
CHARACTERISTICS
P side is connected to negative & n side to positive of the external power
The barrier potential increases as the external voltage.
Depletion layer thickens (widens).
The diode remains non-conducting except for a small drift current (of the
order of a few microampere)
On further increasing, the external voltage the diode breaks down with a
sudden increase in current. This damages the diode. This voltage is known
as break down voltage
A semiconductor Diode(p-n Junction) allows current only in one direction(
Forward Bias).
This property of Diode is used in the construction of a rectifier
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REVERSE BIAS
CHARACTERISTICS
A semiconductor Diode(p-n Junction) allows current only in one direction(
Forward Bias).
This property of Diode is used in the construction of a rectifier
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TIPS TO LEARN PHYSICS
NCERT BOOK was only Reference and Text Book
NCERT Worked Out Examples
NCERT Book Back Exercise (Except Additional Exercise)
Previous Yr. Paper
Reference books:
1. XAM Idea (Board Type)
2. S.L..Arora (Board & Entrance exam)
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REFERENCE
Textbook:
1.NCERT Physics Class 12 Volume 2
2. Electronic Devices and Circuit Theory-By ROBERT BOYLESTAD &
LOUIS NASHELSKY
Website:
1. https://ethw.org/Semiconductors
2.https://www.worldscientific.com/worldscibooks/10.1142/P647
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