Unit 4 Semiconductor Physics handwriting

Dy Sadhana ASaujant
UNIT 4 e e Ne


SEMICONDUCTOR PHYSICS

@1Derlve an expressicn for cenductivity of
conductors +E(elecdsic fiel) AcroG secticral
qea)
Selticn: Let
n+nunbes ef
Clengtb) electyenspe
unit volume
+

In the absence cf electric field,electrons
mOvO Yandemnls in all directions
But wohen an external aletric field is applied.
the random motion becomes directed This
is called dift The dzift velocity of elecon
dependa on the applied electric ield
1=ME -----()
ubheze is electron mebil
But E=V - (2)

-9)

The current Ploeing through the conductor is
given by. I=neA -

I =ne(4y)A fron 3)
R= V )
I neA
The resislivily (8) ot the cenducler is
given by.
= RA
PTO->

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YoUVA
fate




----from5)
|neA

---(6)
ne
The cobductivity_of the_condutor is
given by
6I

=ne




Q: Derive the expression for conductivity of
intinaic and extrinsic semiconductors
Marks)
ÇONDUCTIVITY OF SEMI CONDUCTORS:
I -Aarea ef
isecticn

Coneidex semiconduetox of length )
and cTOSS eectional area A.
Let, n, -eleton densit in condudion bard -
np- bole density in valence band
ua- elecrenmab
mebiltty
bole mobllty
ve -drit velocity of electrons.
tp-dift velacity of boles:
PTO-’

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Date




The total curent through the semicenducor
is given by,
I IetIe

I =ne yAtn,e , A I=neva
I =eA(n_ tTpp){0.
and




R=V=
I
eACneltnpMp
The resistivity B) ot semiconducter is given
by
8=RA


XArom)


Cndetnplp
Hence coneucivitey is qiven by
PTO