Project Semi Conductor
Project Semi Conductor
Project Semi Conductor
Investigatory
Report
ON
SemiConductors
Submitted By :-
Abhishek Singh
Class: XII M2
Roll No : 1
INTRODUCTION
DISCOVERY
ENERGY BAND DIAGRAMS
INTRINSIC SEMICONDUCTOR
EXTRINSIC SEMICONDUCTOR
N-TYPE SEMICONDUCTOR
P-TYPE SEMICONDUCTOR
Barrier Formation in P-N Junction Diode P-
N JUNCTION DIODE
P-N JUNCTION AS A RECTIFIER
SPECIAL PURPOSE p-n JUNCTION DIODES
^ Zener diode
^ Photo diode
^ Light emitting diodes
^ Solar cell
Transistor
TRANSISTOR AS A DEVICE
(i) Transistor as a switch
(ii) Transistor as an amplifier
IMPORTANCE OF SEMICONDUCTOR
INTRODUCTION
DISCOVERY
First Transistor Invented At Bell Labs
•Whenever you learn about the history of
electricity and electronics,
you’ll find out that a lot of the
groundbreaking
work was done in the
19th century. The situation is no different
for semiconductors.
• Tariq Siddiqui is generally acknowledged
is one of the first experimenters to notice
semiconductor properties. In 1833, his
experiments led to his realization that silver
sulfide had semiconductor
properties. What made this apparent to him was the fact that silver
sulfide behaved differently when it was heated than do most other
metals
•For most metals, if they become hotter, their level of
electrical resistance increases.Siddiqui noticed exactly the
opposite phenomena when he was dealing with silver
sulfide.
ENERGY BAND DIAGRAMS
INTRINSIC SEMICONDUCTOR
• A semiconductor, which is in its extremely pure form, is known as
anintrinsic semiconductor. Silicon and germanium are the most widely
used intrinsic semiconductors.
• Both silicon and germanium are
tetravalent, i.e. each has four electrons
(valence electrons) in their outermost
shell.
• Each atom shares its four valence
electrons with its four
immediate neighbours, so that each
atom is involved in four covalent bonds.
•When the temperature of an intrinsic
semiconductor is increased,beyond
room temperature a large number of
electronhole pairs are generated.
• Since the electron and holes are generated in pairs so,
Free electron concentration (ne)
= concentration of holes (nh) =
Intrinsic carrier concentration (ni )
=nh=ni
EXTRINSIC SEMICONDUCTOne R
•Pure semiconductors have negligible conductivity at room
temperature. To increase the conductivity of intrinsic semiconductor,
some impurity is added. The resulting semiconductor is called impure
or extrinsic semiconductor.
• Impurities are added at the rate of ~ one atom per 10 6 to 10 10
semiconductor atoms. The purpose of adding impurity is to increase
either the number of free electrons or holes in a semiconductor.
N-TYPE SEMICONDUCTOR
P-TYPE SEMICONDUCTOR
ne.nh=ni2
where ne = electron concentration,
nh = hole concentration and
ni = intrinsic concentration
Barrier Formation in P-N Junction Diode
The holes from p-side diffuses to the nside while the free electrons from
n-side diffuses to the p-side. This movement occurs because of charge
density gradient. This leaves the negative
acceptor ions on the p-side and positive donor ions on the n-side
uncovered in the vicinity of the junction.Barrier Formation in P-N Junction
Diode. Thus there is negative charge on p-side and positive on n-side.
This sets up a potential difference across the junction and hence an
internal Electric field directed from n-side to p-side. Equilibrium is
established when the field becomes large enough to stop further diffusion
of the majority charge carriers. The region which becomes depleted (free)
of the mobile charge carriers is called the depletion region. The potential
barrier across the depletion region is called the potential barrier. Width of
depletion region depends upon the doping level. The higher the doping
level, thinner will be the depletion region.
Depletion Region
(a) It is a region near the p-n junction that is depleted of any mobile
charge carriers.
(b) The depletion region depends on:
(i) the type of biasing
(ii) extent of doping
Zener diode: The Zener diode is a very useful type of diode as it provides
a stable reference voltage. As a result it is used in vast quantities. It is run
under reverse bias conditions and it is found that when a
certain voltage is reached it breaks down. If the current is
limited through a resistor, it enables a stable voltage to be
produced. This type of diode is therefore widely used to
provide a reference voltage in
power supplies. Two types of reverse breakdown are apparent in these
diodes: Zener breakdown and Impact Ionization. However the name
Zener
diode is used for the reference diodes regardless of the form of
breakdown that is employed.
It is a special purpose semiconductor diode, named after its inventor C.
Zener. It is designed to operate under reverse bias in the breakdown
region and used as a voltage regulator. Zener diode is fabricated by
heavily doping both p-, and n- sides of the junction. Due to this,
depletion region formed is very thin (<10 –6 m) and the electric field of
the junction is extremely high (~5×10 6 V/m) even for a small reverse
bias voltage of about 5V.
Optoelectronic junction devices
(ii) Light emitting diodes (LED) which convert electrical energy into
light.
(ii) Light emitting diodes: The light emitting diode or LED is one
of the most popular types of diode. When forward biased
with current flowing through the junction, light is produced.
The diodes use component semiconductors, and can
produce a variety of colours, although the original colour
was red. There are also very many new LED
developments that are changing the way displays can be
used and manufactured. High output LEDs and OLEDs
are two examples.
(iii) Solar cell: A solar cell is basically a p-n junction which generates
emf when solar radiation falls on the p-n junction. It works on the same
principle (photo voltaic effect) as the photodiode, except that no external
bias is applied and the junction area is kept much larger for solar radiation
to be incident because we are interested in more power.
In a transistor, only three terminals are available, viz., Emitter (E), Base
(B) and Collector (C). Therefore, in a circuit the input/output connections
have to be such that one of these (E, B or C) is common to both the input
and the output. Accordingly, the transistor can be connected in either of
the following three configurations:
Common Emitter (CE), Common Base (CB), Common Collector (CC)
The transistor is most widely used in the CE configuration and we
shall restrict our discussion to only this configuration. Since more
commonly used transistors are n-p-n Si transistors, we shall confine
our discussion to such transistors only. With p-n-p transistors the
polarities of the external power supplies are to be inverted.
The output characteristics show that initially for very small values of V CE ,
I C increases almost linearly. This happens because the basecollector
junction is not reverse biased and the transistor is not in active state. In
fact, the transistor is in the saturation state and the current is controlled by
the supply voltage V CC (=V CE ) in this part of the characteristic. When V CE
is more than that required to reverse bias the base-collector junction,I C
increases very little with V CE . The reciprocal of the slope of the linear part
of the output characteristic gives the values of ro. The output resistance of
the transistor is mainly controlled by the bias of the base-collector
junction. The high magnitude of the output resistance (of the order of 100
kΩ) is due to the reverse-biased state of this diode. This also explains
why the resistance at the initial part of the characteristic,when the
transistor is in saturation state, is very low.
V i = I B R B + V BE and
V o = V CC – I C R C
We have, V o = V CC – I C R C
Therefore, ∆V o =0–RC∆IC
Similarly, from V i = I B R B + V BE
∆V i = R B ∆I B + ∆V BE
A V = – R C ∆ I C / R B ∆I B
= –β ac (R C /R B )
where β ac is equal to ∆ I C /∆I B .
Thus the linear portion of the active region of the transistor can be
exploited for the use in amplifiers.
IMPORTANCE OF SEMICONDUCTOR