1 Notes For 25 February Electron and Hole Concentrations in Extrinsic Semiconductor , exp exp exp ) ( ) ( exp exp 0 kT E E n kT E E kT E E N kT E E E E N kT E E N n Fi F i Fi F c Fi c Fi F Fi c c c F c , exp exp exp ) ( ) ( exp exp 0 kT E E p kT E E kT E E N kT E E E E N kT E E N p F Fi i F Fi Fi v v F Fi Fi v c F v v 2 0 0 exp i g v c n kT E N N p n For both undoped material and doped material under equilibrium condition
1 Notes For 25 February Electron and Hole Concentrations in Extrinsic Semiconductor For both undoped material and doped material under equilibrium condition.
Jan 18, 2016
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1
Notes For 25 February
Electron and Hole Concentrations in Extrinsic Semiconductor
,expexpexp
)()(expexp0
kT
EEn
kT
EE
kT
EEN
kT
EEEEN
kT
EENn
FiFi
FiFcFic
FiFFicc
cFc
,expexpexp
)()(expexp0
kT
EEp
kT
EE
kT
EEN
kT
EEEEN
kT
EENp
FFii
FFiFivv
FFiFivc
Fvv
200 exp i
gvc n
kT
ENNpn
For both undoped material and doped
material under equilibrium condition
2
Position of Fermi Energy in Extrinsic Semiconductors
i
Fi
v
v
i
Fi
c
cF
n
pkTE
N
pkTE
n
nkTE
N
nkTEE
00
00
lnln
lnln
,expexp0
kT
EEn
kT
EENn FiF
icF
c
,expexp0
kT
EEp
kT
EENp FFi
iFv
v
Position of Fermi-level:
3
Position of Fermi Energy in Extrinsic Semiconductors
i
Fi
v
v
i
Fi
c
cF
n
pkTE
N
pkTE
n
nkTE
N
nkTEE
00
00
lnln
lnln
,expexp0
kT
EEn
kT
EENn FiF
icF
c
,expexp0
kT
EEp
kT
EENp FFi
iFv
v
Position of Fermi-level:
44
Variation of Fermi-Energy with Doping Concentration
55
Variation of Fermi-Energy with Temperature
66
Chapter 5 Carrier Transport Phenomena
Charged carriers in semiconductor: electrons and holes
Carrier transport: movement of electrons and holes
Mechanisms of carrier transport
Drift:
Diffusion:
charge movement due to electric field
charge movement due to density gradient
88
Carrier DriftObserve that the text uses “e” instead of “q” as a symbol for a unit of charge
Drift current densityddrift vJ
Current density due to the holesep
Drift velocity of holes Ev pdp
EenJ ntdrifn
Current density due to the holes
Current density due to the electrons
EepJ ptdrifp
Drift velocity of electrons Ev ndn
Total drift current density EnpeJ npdrift )(
Charge density:
Charge density: en
99
Definition of Carrier Mobility
Ev pdp Drift velocity of holes
Drift velocity of electrons Ev ndn
p : mobility of holes
n : mobility of electrons
Mobility: relates the average drift velocity of a carrier to the electric field
1010
Conductivity
EEnpeJ npdrift )(
)( np npe Conductivity:
Resistivity:
Unit: (Ω.m)-1
)(
11
np npe
Unit: (Ω.m)
N-type semiconductor:ndnnp eNennpe )(
P-type semiconductor:papnp eNepnpe )(
Intrinsic semiconductor: )()( npinp ennpe
1414
Resistance
A
IJ
L
VE
EJ
L
V
A
I RIIA
LI
A
LV
A
L
A
LR
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