• 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
INTRODUCTIONCONDUCTORS: 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. semiconductor will behaves as insulators and at high temperature, They willbehaves as conductors. E.G :Germanium , Silicon
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 toconduction band . As a result of it vacancy is created in the valence band at aplace 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 conductors1 Intrinsic semi conductors: The semi conductors which is free from every type ofimpurity is called intrinsic semi conductors. e.g.siliconRelation 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
EXTRINSIC SEMI CONDUCTOR A semi conductor with suitable impurity atoms are added to it is called anextrinsic semi conductors . The impurity atoms are added to pure semi conductor inorder to increase its conductivity.EXTRINSIC SEMI CONDUCTOR ARE OF TWO TYPES1)N – TYPE SEMI CONDUCTORS2)P-TYPE SEMI CONDUCTORS
N-TYPE SEMI CONDUCTORS In case of silicon the electronic configuration is 1s2 2s2 2p6 3s2 3p2silicon atom has four valence electrons and hence silicon atom make covalent bond withother 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
C.B empty Eg Occupied donour V.B levels Completely filledN-TYPE semi conductors , the numberof electrons into the conduction band are morethan the number of holes into the valence band . N-TYPE semi conductors electrons are the majority carriers and holes are theminority carriers (ne>>nh) but nenh=ni2
P-TYPE SEMI CONDUCTORIn case of silicon the electronic configuration is 1s2 2s2 2p6 3s2 3p2 siliconatom has four valence electrons and hence silicon atom make covalent bond with othersilicon atoms . Hence add very small amount of In to silicon crystal . Si Si Si holes Si In Si holes Phosphorous atoms Si Si Si
The impurity atoms added to a pure semiconductors is trivalent is that which havethree electrons in their outer most shell ,thenthe semi conductors obtained is called P- C.BTYPE semi conductors. empty Eg atteptor energy levels V.B Completely filledIn P-TYPE semi conductor holes are the majority carriers and electrons are the minoritycarriers .nh>ne & nenh=ni2 .
DIFFERENCE BEETWEEN INTRINSIC SEMI CONDUCTOR & EXTRINSIC SEMI CONDUCTORINTRINSIC SEMI CONDUCTOR EXTRINSIC SEMI CONDUCTOR1)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 conductor2)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=nh3) 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 silicongermanium. germanium containing impurities like As , In, B, Al etc.
SEMI CONDUCTOR DEVICES P NP-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
DIODE : “The electronic devices consisting of a P-N junction is called a diode.” Symbolically P-N junction
BIASING ON P-N JUNCTIONThere are two method of biasing on P-N junction1)FORWARD BIASING2) REVERSE BIASING1) 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 PSide and negative terminal of the battery is connected to the N side of an P-Njunction. V - B+ - P-TYPE N-TYPE + - + - + - + - - + + + + - - - + Depletion Layer V
2)REVERSE BIASING : A P-N junction is said to be reverse biased ,if +ve terminal ofthe external battery is connected to the N- side and negative terminal is connected to theP-side of the P-N junction. VB - + - P-TYPE N-TYPE + - + - + - + - - + + + + - - - + Depletion Layer V
CHARACTERISTICS OF A P-N JUNCTION DIODES1)FORWARD CHARACTERISTICS BForward current(milli ammeter) A O Knee voltage (vk)
2)REVERSE CHARACTERISTICBreak downvoltage Reverse bias O Reverse current A (microammeter ) B
ADVANTAGE OF SEMI CONDUCTOR DEVICES1) Semi conductor are much smaller in size and weight ascompared to vacuum tube.2)Semi conductor devices are not to be heated for emission ofelectrons.3)Semi conductor devices have much longer life as compared tothe life of vacuum tubes.4)Semi conductor devices are cheaper than vacuum tube devices.5)Semi conductor devices are low power devices and operate atlow voltage.
DISADVANTAGE OF SEMI CONDUCTOR DEVICES1)Semi conductor devices are very sensitive to change oftemperature whereas the vacuum tube are less sensitive.2)The noise level in semi conductor devices is higher than ofvacuum tubes.3)Semi conductor can not handle as much power as vacuumtubes.4)It is very difficult to produce identical semi conductor devices.