2. • INTRODUCTION
• DISTINGUISH B/W SEMI CONDUCTOR , CONDUCTOR &
INSULATOR
•FORMATION OF HOLES IN SEMI CONDUCTOR
• TYPES OF SEMI CONDUCTOR
• SEMI CONDUCTOR DEVICES
• ADVANTAGES OF SEMI CONDUCTOR
• DISADVANTAGES OF SEMI CONDUCTOR
3. INTRODUCTION
CONDUCTORS: These are the materials which conduct current at every
Temperature.
INSULATORS : These are the materials which does not conduct electric
current.
SEMI CONDUCTOR: These are materials which are in between
conductors and insulators. At low temp. semi
conductor will behaves as insulators and at high temperature, They will
behaves as conductors.
E.G :Germanium , Silicon
4. FORMATIONS OF HOLES INTO THE SEMI CONDUCTORS
C.B C.B
Eg Eg
V.B V.B
(At zero kelvin) At room temp.
At room temp. some of the electrons will moves from valence band to
conduction band . As a result of it vacancy is created in the valence band at a
place where electron was present . “This vacancy is called a hole”
5. TYPES OF SEMI CONDUCTORS
These are two types
1)Intrinsic semi conductors
2)Entrinsic semi conductors
1 Intrinsic semi conductors: The semi conductors which is free from every type of
impurity is called intrinsic semi conductors. e.g.silicon
Relation b/w nh , ne & ni is nenh=ni2
Si Si Si C.B
empty
Free e-
Si Si Si V.B
Completely filled
Si Si Si
6. EXTRINSIC SEMI CONDUCTOR
A semi conductor with suitable impurity atoms are added to it is called an
extrinsic semi conductors . The impurity atoms are added to pure semi conductor in
order to increase its conductivity.
EXTRINSIC SEMI CONDUCTOR ARE OF TWO TYPES
1)N – TYPE SEMI CONDUCTORS
2)P-TYPE SEMI CONDUCTORS
7. N-TYPE SEMI CONDUCTORS
In case of silicon the electronic configuration is 1s2 2s2 2p6 3s2 3p2
silicon atom has four valence electrons and hence silicon atom make covalent bond with
other silicon atoms . Hence add very small amount of P to silicon crystal .
Si Si Si
Free e-
Si P Si
Phosphorous
atoms
Si Si Si
8. C.B
empty
Eg Occupied
donour
V.B levels
Completely filled
N-TYPE semi conductors , the numberof electrons into the conduction band are more
than the number of holes into the valence band .
N-TYPE semi conductors electrons are the majority carriers and holes are the
minority carriers (ne>>nh) but nenh=ni2
9. P-TYPE SEMI CONDUCTOR
In case of silicon the electronic configuration is 1s2 2s2 2p6 3s2 3p2 silicon
atom has four valence electrons and hence silicon atom make covalent bond with other
silicon atoms . Hence add very small amount of In to silicon crystal .
Si Si Si
holes
Si In Si
holes Phosphorous
atoms
Si Si Si
10. The impurity atoms added to a pure semi
conductors is trivalent is that which have
three electrons in their outer most shell ,then
the semi conductors obtained is called P- C.B
TYPE semi conductors. empty
Eg atteptor
energy levels
V.B
Completely filled
In P-TYPE semi conductor holes are the majority carriers and electrons are the minority
carriers .nh>ne & nenh=ni2 .
11. DIFFERENCE BEETWEEN INTRINSIC SEMI CONDUCTOR & EXTRINSIC
SEMI CONDUCTOR
INTRINSIC SEMI CONDUCTOR EXTRINSIC SEMI CONDUCTOR
1)It is a pure semi conductor without 1)It is prepared by doping a small quantity of
any impurity in it. impurity atoms to a pure semi conductor
2)In the intrinsic semi conductor the 2)In extrinsic semi conductor the number
number of free electrons in the of free electrons and so holes are never
conduction band and the number of equal . There is an excess of electrons in
holes in the valence band are exactly the N-TYPE semi conductor
equal. E.g ne=nh
3) Its electrical conductivity is very 3) Its electrical conductivity is very
low. high.
4) Its electrical conductivity is a function 4) Its electrical conductivity depends upon
of temperature alone the temp. as well as on the quantity of
the impurity atoms doped in the structure.
5)It is not much useful. 5) It has number of application in electronics.
6)Examples are the crystalline forms 6) Examples are crystals of silicon & of silicon
germanium. germanium containing impurities like
As , In, B, Al etc.
12. SEMI CONDUCTOR DEVICES
P N
P-N JUCTION : When P-TYPE crystals is brought in + + - -
contact with N-TYPE crystals , the resulting arrangement - +
is called a P-N JUNCTION or JUCTION DIODES . + + - -
VB
- +
-
P-TYPE N-TYPE
+ - + -
+ - + -
- +
+ + + - -
- +
Depletion Layer
13. DIODE : “The electronic devices consisting of a P-N junction is called a diode.”
Symbolically P-N junction
14. BIASING ON P-N JUNCTION
There are two method of biasing on P-N junction
1)FORWARD BIASING
2) REVERSE BIASING
1) FORWARD BIASING : In P-N junction is said to be in the forward biasing , if the
positive terminal of the external battery is connected to P
Side and negative terminal of the battery is connected to the N side of an P-N
junction. V
- B+
-
P-TYPE N-TYPE
+ - + -
+ - + -
- +
+ + + - -
- +
Depletion Layer
V
15. 2)REVERSE BIASING : A P-N junction is said to be reverse biased ,if +ve terminal of
the external battery is connected to the N- side and negative terminal is connected to the
P-side of the P-N junction.
VB
- +
-
P-TYPE N-TYPE
+ - + -
+ - + -
- +
+ + + - -
- +
Depletion Layer
V
16. CHARACTERISTICS OF A P-N JUNCTION DIODES
1)FORWARD CHARACTERISTICS
B
Forward current
(milli ammeter)
A
O
Knee voltage (vk)
20. ADVANTAGE OF SEMI CONDUCTOR DEVICES
1) Semi conductor are much smaller in size and weight as
compared to vacuum tube.
2)Semi conductor devices are not to be heated for emission of
electrons.
3)Semi conductor devices have much longer life as compared to
the life of vacuum tubes.
4)Semi conductor devices are cheaper than vacuum tube devices.
5)Semi conductor devices are low power devices and operate at
low voltage.
21. DISADVANTAGE OF SEMI CONDUCTOR DEVICES
1)Semi conductor devices are very sensitive to change of
temperature whereas the vacuum tube are less sensitive.
2)The noise level in semi conductor devices is higher than of
vacuum tubes.
3)Semi conductor can not handle as much power as vacuum
tubes.
4)It is very difficult to produce identical semi conductor devices.
