Naveen Sihag

• 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

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

FORMATIONS OF HOLES INTO THE SEMI CONDUCTORS

C.B C.B

V.B V.B

Eg Eg

(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”

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

Free e-

C.B empty

V.B Completely filled

Si

Si

SiSi

Si

SiSi

SiSi

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

Free e-

Si

SiSiSi

Si

Si

Si

SiP

Phosphorous

atoms

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 .

C.B empty

V.B Completely filled

Occupied

donour levels

Eg

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

Si

SiSiSi

Si

Si

Si

SiIn

Phosphorous

atoms

holes

holes

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 .

C.B empty

V.B Completely filled

atteptor

energy levels Eg

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-TYPE semi conductors.

In P-TYPE semi conductor holes are the majority carriers and electrons are the minority carriers .nh>ne & nenh=ni2 .

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.

SEMI CONDUCTOR DEVICESP 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 .

--++

--++

+++

++

----

P-TYPE N-TYPE

--+

V B

Depletion Layer

DIODE : “The electronic devices consisting of a P-N junction is called a diode.”

Symbolically P-N junction

BIASING ON P-N JUNCTION

There are two method of biasing on P-N junction

1)FORWARD BIASING

2) REVERSE BIASING

1) FORWARD BIASING :

--++

--++

+++

++

----

P-TYPE N-TYPE

--+

V B

Depletion Layer

V

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.

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.

--++

--++

+++

++

----

P-TYPE N-TYPE

--+

V B

Depletion Layer

V

CHARACTERISTICS OF A P-N JUNCTION DIODES

1)FORWARD CHARACTERISTICS

Knee voltage

A

B

O(vk)

Forward current

(milli ammeter)

2)REVERSE CHARACTERISTIC

Reverse current

(microammeter )

Reverse bias

A

B

O

Break down voltage

P-N JUNCTION AS A HALF WAVE RECTIFIER

P-N JUNCTION AS FULL WAVE RECTIFIRE

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.

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.