PHYSICS PROJECT FOR CBSE CLASS 12TH

1. PHYSICS PROJECT
ON
SEMICONDUCTORS
In The Able Guidance Of
Miss S. Nath
(PGT Physics)
Presented By-
Subhendra Kumar Satapathy
Roll. No. - 6103290
CLASS- XII
JAWAHAR NAVODAYA VIDYALAYA
TARBHA, SONEPUR, ODISHA

2. SEMICONDUCTOR
This is to certify that Master Subhendra Kumar Satapathy of
Class-XII-Sc. has successfully carried out the project entitled
“Semiconductors” under the proper guidance and supervision of
Miss S. Nath, PGT Physics in the academic year 2015-16.
This project is absolutely genuine and does not indulge in
plagiarism of any kind. The observations are apt and the
information is correct. The project has fulfilled all the conditions to
the best of my knowledge and information. The project embodies
to my originalwork.
Signature of the Internal Examiner Signature of the External Examiner
Principal

3. SEMICONDUCTOR
ACKNOWLEDGEMENT
I am grateful to almighty for giving me the strength to
successfully conduct my experiment and for sustaining my efforts
which many a times did oscillate.
I am deeply indebted to Miss S. Nath, our Physics Madam,
without whose constructive guidance this project would not have
been a success. Her valuable advice and suggestion for the
correction, modifications and improvements did enhance the
perfection in performing my job well.
I am obliged to Miss S. Kumar, our F.C.S.A. and Mr. C. S. A.
Bharti, our Librarian for providing the best facilities and
environment to bring out our innovation and spirit of inquiry
through this venture.
I take special pleasure in acknowledging Master Biswajit Panda
for constant support without which my effort would have been
worthless.
At last but not the least I thank all my Friends and my Batch
Mates, without their prompt support my efforts would have been
in vain.
Subhendra Kumar Satapathy

4. SEMICONDUCTOR
1. INTRODUCTION
2. ELECTRICITY
3. CONDUCTIVITY
4. ELECTRON HOLE
PAIR
5. DOPING
INTRODUCTION

5. SEMICONDUCTOR
Let's begin this journey into the world of semiconductors with a look at the
history books. In the early 1900s, not much was known of the world at an
atomic level and even less so at the subatomic level. Physics, to a large
extent, still calmly followed classical rules.
Thomson's electron and discovery of the atomic nucleus made it clear that
new rules were needed. Scientists have contributed to the development
and understanding necessary for the creation of the new paradigm of
quantum physics. The development of quantum physics also laid the ground
for 'Solid State Physics' which is a discipline explaining the internal atomic
structure and the electronic properties of the materials that we see in our
everyday life such as metals, plastics, glass, etc.
The new ways of looking at physics came in handy in 1947. Following in the
footsteps of their predecessors, William Shockley, John Bardeen and Walter
Brattain made their breakthrough discovery of the transistor effect by
constructing the first crude transistor. A vital part of this invention was the
semiconductor and the theory behind it. In 1956 the trio got the Nobel Prize
in Physics for their researches on semiconductors and their discovery of the
transistor effect.
Since then semiconductor devices have evolved tremendously. Today
transistors are extremely small and come packed in millions onto tiny
Silicon chips called integrated circuits. The integrated circuit was invented
by Jack Kilby and Robert Noyce. This invention is essential for digital
technologies like computers, mobile phones, CDs, mp3s or DVDs. The list
could be made almost infinite. For instance, without semiconductor
technology there would be no internet.
ELECTRICITY

6. SEMICONDUCTOR
Before we start, it would be a good idea
to clarify what electricity is. Electricity can
be seen as a stream of electrons.
Electrons are tiny particles with a
negative charge. So, roughly explained,
electricity is a stream of electrons flowing
from one point to another.
CONDUCTIVITY
The word conductivity is used to describe a material’s ability to transport
electricity. This ability varies in different materials. Metals, like copper and
gold, are good conductors. Glass or plastics, on the other hand, are very bad
conductors. In fact, they don’t conduct at all. Materials that don’t conduct
current are called insulators. Semiconductors, like silicon, are materials with
conductivity somewhere between good conductors and insulators.
Semiconductors can be made of a single material or a combination of
several different materials. In early semiconductor devices germanium was
often used. However in today's semiconductor industry, silicon is commonly
used.
One of the main reasons for the popularity of silicon is that it is stable and
can be heated to a rather high degree without losing its material

7. SEMICONDUCTOR
characteristics. This means that engineers can be sure it will perform
according to their plans, even under quite extreme conditions.
If we look at the solid material of Silicon we will see that it is built from a
huge number of Silicon atoms that are brought together. When the atoms
interact with each other, the atomic shell of each atom interacts with the
atomic shells of neighbouring atoms. On an energy scale, the overlapping
energy shells of all the separate atoms form energy bands that are similar to
the energy shells in the single atom. Between the bands no electrons are
allowed. In a simplified way, it is almost as if the solid material is an
enlargement of the single atom.
ELECTRON HOLE PAIR
A very important feature of the semiconductor material is the electron-hole
pair. To get a semiconductor to conduct a current, we must make an
electron jump from an occupied to an unoccupied energy level. When it
does this it leaves a hole (an empty state). This hole can be filled by another
electron, which itself leaves a new hole. Therefore, we could say that both
the hole and the electron contribute to the conductivity as they move
around in the material. The hole is like a positive charge (lack of negative),
the electron is negative.

8. SEMICONDUCTOR
As mentioned earlier, the semiconductor has a conducting capacity
somewhere between the conductor and the insulator. If we look closer at
the materials we can see why they behave like this. Before we go on, note
that contrary to what its name may suggest, the conduction band is not the
only band where conduction of a current may occur. Conduction is equally
possible in the valence band.
DOPING
Now we are going to talk about doping. Maybe the word makes you think of
athletes taking illegal drugs to perform better. Although doping in sports is
outrageous, the parallel between that and doping of semiconductors is not
too far-fetched. In both cases you have something pure, like an athlete or a
semiconducting material, and add something foreign to it to change its
performance.
So, in the process of doping you add a
tiny amount of atoms from another
material to the pure semiconductor. By
doing so, you can drastically increase its
ability to conduct a current. There are
two forms of doping, p and n. p stands
for positive and n for negative. Finally,
two words that are good to know: a
pure non-doped semiconductor is called intrinsic, while a doped
semiconductor material is called extrinsic.

9. SEMICONDUCTOR
Before we look at examples of doped semiconductors, let's look at how the
silicon atoms in pure silicon interact to form the crystal structure of the
material. In pure silicon, each atom has four valence electrons and these are
shared with four neighbouring silicon atoms to make four double bonds.
Now each atom will have a completely filled valence shell of eight electrons.
At low temperature this bond is very stable, completely filling the valence
band and thus making
conduction impossible. Here is
a model of the structure of
pure silicon:
In a pure semiconductor at low
temperature, the valence layer
is completely filled with
electrons and the conduction
band is empty. That would be equal to one filled and one empty
compartment in my cup. The water (electrons) can't move because there is
no empty space.
P-Doping is when you add atoms with less valence electrons to the
semiconductor so that the material gets a shortage of electrons in the
crystal bonds. This way positive holes that can transport current are
formed. The materials that add holes are called acceptors because they
accept electrons from the surrounding atoms. In a p-type semiconductor
the major carrier of current are the holes, not the electrons.
The p in p-doping stands for
positive. This is because
compared to the atoms in the
semiconductor material the
added atoms have fewer negative
valence electrons. In the p-doped
semiconductor the higher
conduction band is empty, but
there will be holes in the valence
band.
In the cup, this means that we remove some water from the valence
compartment. In other words, we form air bubbles (positive holes) in the

10. SEMICONDUCTOR
water. Now if we tip the cup, there is room for the water (electrons) to
move in one direction and for the created holes (lack of electrons) to move
in the opposite direction (just like bubbles would do in water).
In the process of N-Doping you add atoms with one extra valence electron
to the pure semiconducting material. This creates a situation where there
are extra electrons that are just loosely bound in the crystal. The amount of
energy needed to get these electrons to jump to the conduction band so
that a current may pass is very small. The materials that add electrons are
called donors. This is simply because they donate electrons to the
semiconductor. In the n-type semiconductor the major carrier of current is
the negative electrons.
The n in n-doping stands for
negative. This is because
compared to the atoms in the
semiconductor material the
added atoms have more
negative valence electrons. In
the n-doped semiconductor,
the valence band is full so there
is no room for the electrons to
move there. Instead, the extra electrons move into the conduction band.
In our cup, we can see that no water will move in the full valence
compartment. Instead, the extra water (electrons) added will move within
the conduction compartment.

11. SEMICONDUCTOR
BOOKS
 NCERT TEXT BOOK IN PHYSICS FOR CLASS XII
 PRADEEPTEXT BOOK IN PHYSICS
 DINESH PHYSICS TEXT BOOK
 MTG EXCEL IN PHYSICS
 COMPLEMENTARY PHYSICS
 INTRODUCTORYPHYSICS
 PHYSICS TODAY
 PHYSICS SPECTRUM
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 WIKIPAEDIA THE FREE ENCYCLOPAEDIA
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