notes for 25 february electron and hole concentrations in extrinsic semiconductor
DESCRIPTION
Notes For 25 February Electron and Hole Concentrations in Extrinsic Semiconductor. For both undoped material and doped material under equilibrium condition. 1. Position of Fermi Energy in Extrinsic Semiconductors. Position of Fermi-level:. 2. - PowerPoint PPT PresentationTRANSCRIPT
1
Notes For 25 February
Electron and Hole Concentrations in Extrinsic Semiconductor
,expexpexp
)()(expexp0
kTEEn
kTEE
kTEEN
kTEEEEN
kTEENn
FiFi
FiFcFic
FiFFicc
cFc
,expexpexp
)()(expexp0
kTEEp
kTEE
kTEEN
kTEEEEN
kTEENp
FFii
FFiFivv
FFiFivc
Fvv
200 exp i
gvc n
kTE
NNpn
For both undoped material and doped
material under equilibrium condition
2
Position of Fermi Energy in Extrinsic Semiconductors
iFi
vv
iFi
ccF
np
kTENp
kTE
nn
kTENn
kTEE
00
00
lnln
lnln
,expexp0
kTEE
nkTEE
Nn FiFi
cFc
,expexp0
kTEEp
kTEENp FFi
iFv
v
Position of Fermi-level:
3
Position of Fermi Energy in Extrinsic Semiconductors
iFi
vv
iFi
ccF
np
kTENp
kTE
nn
kTENn
kTEE
00
00
lnln
lnln
,expexp0
kTEE
nkTEE
Nn FiFi
cFc
,expexp0
kTEEp
kTEENp 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
AIJ
LVE
EJ
LV
AI RII
ALI
ALV
AL
ALR