WHILE UPLOADING SOME CHANGES ARE HAPPENED IN FRONT PAGE.I FACED MANY PROBLEMS TO COMPLETE THIS PROJECT.BECAUSE NO ONE HAD DONE THIS PROJECT BEFORE SO, IN ORDER TO AVOID OTHERS TO FACE SAME PROBLEM WHICH I FACED KEPT THIS EXAMPLE WHICH HELP YOU ALL.HOPE IT WILL HELPS YOU.

1. pHYSICS inESTIGATORY
PROJECT
Topic:semiconductors&diodes
name- E.SaiCharan Kumar Netha
Class-xii rollno-1217
kendriyavidyalayano2uppal 2015-2016

2. INDEX
1.INTRODUCTION
2. INTRINSIC SEMICONDOCTORS
3. EXTRINSIC SEMICONDUCTOR
4. P-TYPE SEMICONDUCTOR
5. N-TYPE SEMICONDUCTOR
6. APPLICATIONS OF SEMICONDUCTOR
7. DIODES
8. BIBLIOGRAPHY

3. KENDRIYA VIDYALAYA No2 UPPAL HYD
DEPARTMENT OF PHYSICS
CERTIFICATE
This is to certify thatE.SAI CHARAN KUMAR
NETHA, a student of class XII-A has successfully
completed the project titled “SEMI CONDUCTORS
&DIODES” under the guidance of N.V.N.GOPALA
KRISHNA RAO P.G.T-Physicsduring the academic year
2015-16 in partial fulfillment of physics practical
examination conducted by AISSCE, HYDERABAD
R Sankar N.V.N.Gopala Krishnarao
Principal P.G.T-Physics

4. ACKNOWLEDGEMENT
In the accomplishment of this project successfully, many
people have best owned upon me their blessings and the
heart pledged support, this time I am utilizing to thank
all the people who have been concerned with project.
Primarily I would thank god for being able to complete this
project with success. Then I would like to thank my principal
Mr.R.SANKAR and physics teacher Mr.N.V.N.GOPALA
KRISHNA RAO whose valuable guidance has been the ones
that helped me patch this project and make it full proof
success his suggestions and his instructions has served as the
major contributor towards the completion of the project.
Then I would like to thank my parents and friends who have
helped me with their valuable suggestions and guidance has been
helpful in various phases of the completion of the project.
E.SAI CHARAN KUMAR NETHA

5. Introduction
Semiconductor
A semiconductor is a material which has electrical
conductivity to a degree between that of
a conductors (such as copper) and that of
an insulator (such as glass). Semiconductors are the
foundation of modern electronics,
including transistors, solar cells, light-emitting
diodes (LEDs), quantum dots and digital and
analog integrated circuits.
A semiconductor may have a number of unique
properties, one of which is the ability to change
conductivity by the addition of impurities ("doping") or
by interaction with another phenomenon, such as
an electric field or light; this ability makes a
semiconductor very useful for constructing a device that
can amplify, switch, or convert an energy input. The
modern understanding of the properties of a

6. semiconductor relies on quantum physics to explain the
movement of electrons inside a lattice of atoms
Carbon, silicon, germanium and tin are atoms in ascending
order of atomic number from column IV A of the period
table. Each is characterised by having four valence
electrons in its outermost shell of electrons, and requires
a further four to make up the full complement of the
shell. All can solidify to form elemental, covalently
bonded crystals where the four valence electrons of one
atom are shared between its four nearest neighbours so
that every atom effectively gains eight electrons in its
valence shell. A group IV atom and its four nearest
neighbours from a tetrahedron as shown in
Figure 1.
Figure 1: Schematic diagram to show the
orientation of covalently bonded group 4
atoms. A tetrahedron is formed by the
nearest neighbours, with the principal atom located at
its centre.
Taking a larger scale perspective of the arrangement of
the atoms, or crystal lattice , it is found that they
organise themselves into two interpenetrating face

7. centred cubic (fcc) sub-lattices, one displaced from the
other by 1/4(a 0 , a 0 , a 0 ) along a diagonal of
the unit cell . a 0 is called the lattice
constant or lattice parameter and is a measure of the
size of the unit cell, often expressed in Angstrom (A)
units (1A=0.1nm or 1x10 -10 m). It is determined by
techniques such as X-ray diffractometry. Figure 2 shows
a complete unit cell for a group 4 crystal covalently
bonded with the diamond structure.
Figure 2: Unit cell of a crystal such as silicon or
germanium
This structure is of course difficult to visualise and draw,
hence it is usually represented by an equivalent 2-D,
"square" arrangement shown in figure 3.

8. Figure 3: 2-D representation of a covalently bonded
crystal at 0K, eg Si.
Note that the heavy lines between adjacent atoms depict
the covalent bonds which contain TWO electrons and
are all completely filled.
DIODES
Invented in 1904 by John Ambrose Fleming.
Was constructed with 2 electrodes in the form
vacuumtube.
In 1906, Lee Dee Forest added a 3rd electrode called
a
control grid and the triode, which is used as
amplifier, switch. The
application of triode created a new era broadcasting
with the invention of the crystal radio sensor by

9. Pickard, 1912.
 Commonly used in DC power supply units as a rectifiers
Comes in different shape and sizes and voltage regulators,
clipper, clamper circuit.
EXTRINSIC SEMICONDUCTORS
One of the key reasons why semiconductors are
technologically so useful is that their electrical, and to a
certain extent their optical properties can be dramatically
modified by the addition of trace concentrations of
impurities. This is true for a wide range of elemental and
compound semiconductors. Although the summary which
follows specifically addresses silicon, the general thrust of
the arguments may be applied to other group IV, III-V
and II-VI materials with due regard for the valency
of the host atoms and impurities.

10. P-Type semiconductors
Neither pure silicon(Si) nor germanium(Ge) are great
conductors. They form a crystal lattice by having each
atom share all of its 4 valence electrons with
neighbouring atoms.
The total of eight electrons can not easily be jiggled out
of place by an incoming current. If the crystalline array
is “doped”(mixed with an impurity) with Boron, which
has five valence electrons, the behaviour of the lattice
will change. Three bonds will be be made and there will
be a deficiency of one, which makes the positive charge
wander through the crystal.
This is called a P-Type Semiconductor, “P” meant for
“Positive”.
N-Type Semiconductors
If the crystalline array is doped with arsenic which has
five valence electrons, the behaviour of the lattice will

11. change. Four bonds will be still be made but there will be
a leftover electron that can wander through the crystal.
This is called N-Type
Semiconductor, “N” for “negative”.
Intrinsic Semiconductors
Returning now to silicon; it has been noted that it is an
insulator at 0K. This is because there is insufficient
energy available from the lattice to cause a covalent bond
to break, so there are no free charges. However, as the
temperature of the crystal is raised, there is a finite

12. probability that a small concentration of bonds will gain
enough energy to break, releasing an electron to become
a free, conduction band electron, while at the same time
leaving behind an unfilled covalent bond (empty state in
the valence band ) which in turn can meander around the
lattice. This unfilled bonded is called a hole and
mathematically is treated as a positive charge (see figure
below).
E g is the forbidden energy gap, or bond strength, of
the semiconductor, which on an energy band diagram is
the energy separation between the conduction and
valence bands; k B is Boltzmann's constant. The equation
arises from rigorous derivations which take account of the
quantum mechanical or wave-like nature of the electrons;

13. and
Applications of Semiconductors
Semiconductors are of enormous technological importance
because of their special properties, which can be modified
by doping. Some applications include:
Thermistors
The resistivity of semiconductors varies with
temperature. This enables semiconductors to be used as
thermometers. Through doping the appropriate sensitivity
in the required ranges can be obtained.
Hall Probes
These measure magnetic field strengths by using a small
piece of semiconductor with known properties. By
measuring the induced Hall voltage in an unknown
magnetic field we can find B using:

14. IR Sensors/Optoelectronic devices
Optoelectronic devices are capable of sensing or
responding to light of various wavelengths. This is due to
the phenomenon of photo-conductivity whereby a
semiconductor can greatly increase its electrical
conductivity if the radiation has sufficient energy to
promote electrons across the band gap. Many different
semiconductors are available with different band gaps to
suit particular applications.

15. DIODES
 The polarity of applied
voltage which causes charge to
flow through the diode is
called Forward Bias. (all
current, almost no voltage)
 The polarity of applied
voltage which can't
produce any current is called
reverse Bias.(all volts, almost
no current)

16. ..AA

17. APPLICATIONS OF DIODES
INDIA
IN
INDIA
INDIA
INDIA INDIA

18. BIBLIOGRAPHY:
HELP FROM INTERNET HELP FROM TEACHER
WESITES
(i)www.google.com
(ii)www.wikipedia.com
(iii)www.slideshare.com