Prof. Junqiao Wu Department of Materials Science and Engineering, U.C. Berkeley
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1 Prof. Junqiao Wu Department of Materials Science and Engineering, U.C. Berkeley [email protected] , 322 HMMB, 510-642-4391 Summer Lectures on Semiconductor Physics for Engineers Contents: 1. Semiconductor basis (2 lectures, 6/2, 6/4) General trends, k-space, band structure, density of states and Fermi distribution kp theory, defects and effective mass approximation Quantum confinement and nanostructures 2. Electrostatics (2 lectures, 6/8, 6/11) Maxwell equations and Poisson’s equation Band bending and carrier equilibration 3. Electrodynamics (2 lectures, 6/16, 6/18) Drude’s model and classical dielectric theory Boltzmann transport theory 4. Thermal effects (2 lectures, 6/23, 6/25) Phonons and thermal physics Thermoelectrics 5. Optical effects (1 lecture, 6/30) Light-semiconductor interactions Device physics of light emitting diodes and solar cells Prerequisites: calculus, vectors, ordinary and partial differential equations, linear algebra, electromagnetism, optics basics, solid state physics basics, quantum mechanics basics Time and location: Tuesday and Thursdays 5:00-6:30PM, June 2009. Rm350, HMMB. Website: http://www.mse.berkeley.edu/~jwu/courses/semi.html
description
Summer Lectures on Semiconductor Physics for Engineers. Prof. Junqiao Wu Department of Materials Science and Engineering, U.C. Berkeley [email protected] , 322 HMMB, 510-642-4391. Contents: Semiconductor basis (2 lectures, 6/2, 6/4) - PowerPoint PPT Presentation
Transcript of Prof. Junqiao Wu Department of Materials Science and Engineering, U.C. Berkeley
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Prof. Junqiao Wu
Department of Materials Science and Engineering, U.C. Berkeley
[email protected], 322 HMMB, 510-642-4391
Summer Lectures on
Semiconductor Physics for Engineers
Contents: 1. Semiconductor basis (2 lectures, 6/2, 6/4)
General trends, k-space, band structure, density of states and Fermi distributionkp theory, defects and effective mass approximationQuantum confinement and nanostructures
2. Electrostatics (2 lectures, 6/8, 6/11)Maxwell equations and Poisson’s equationBand bending and carrier equilibration
3. Electrodynamics (2 lectures, 6/16, 6/18)Drude’s model and classical dielectric theoryBoltzmann transport theory
4. Thermal effects (2 lectures, 6/23, 6/25)Phonons and thermal physicsThermoelectrics
5. Optical effects (1 lecture, 6/30)Light-semiconductor interactionsDevice physics of light emitting diodes and solar cells
Prerequisites:calculus, vectors, ordinary and partial differential equations, linear algebra, electromagnetism, optics basics, solid state physics basics, quantum mechanics basics
Time and location:Tuesday and Thursdays 5:00-6:30PM, June 2009. Rm350, HMMB.
Website: http://www.mse.berkeley.edu/~jwu/courses/semi.html
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s2p2
cation and anion
Most common semiconductors: group IV (Si), III-V (GaAs), II-VI (CdSe), and their alloys
Insulators: group I-VII (NaCl)
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General trends in semiconductors
1.0
1.5
2.0
2.5
3.0
3.5
0 10 20 30 40 50
ele
ctro
ne
ga
tivity
(e
V)
atomic number
Gordy, et. al.J. Chem. Phys.24(2), 439(1956)
O
SSe
N
B
C
P Te
Sb
As
Zn
Mg
Be
Si
GaAlSn
Ge
InCd
covalent
ionic
4
bandgap
Conduction bands
Valence bands
simple cubic face-center cubic zincblende
Brillouin zone(for fcc structure)
5You won’t regret visitinghttp://www.ioffe.ru/SVA/
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n-doped
p-doped
Fer
mi
Si
7
Defects in semiconductors
8
9
Band offsets
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Schottky Contact: example of M/nS with M>S
qM
qS q
ECB
EVB
EFM
EFS
before contact
qM
qS
q
ECB
EVB
EFM EFS
after contact
qVi=q(M-S)
qViqB
-
-
WD
i
qN
VW
2
-- + +-+
-+
vacuumlevel
- -+ +
-+
-+
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Ohmic contact
Work function
12
net charge distribution
S D
nanowire
oxidegate
air
Nano Lett.; 7, 2778 (2007).
8
10
12
14
16
18
20
22
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2
npN
d
log(
conc
entr
atio
n) (
cm-3
)
V (V)
DO
S (
1021
eV
-1cm
-3)
E (eV)
0
2
4
6
8
-2 -1 0 1
VBCB
Si @ 300K
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p-n junction and depletion width
+ + + + +- - -
-----+ + +EF
-
-
+
+ ionized donor
ionized acceptor
free electron
free hole
+
- +-+-
+ -
-++ - +
--
--
---+++
++ +
-+
n-type p-type
ND NA
+
- +-+-
+ -++ - + -
--
---++
++ +
-dx
dnqDJ n
diffn diffusion current
+ + + + +- - - - -
-----+ + + + +
EFn
EFp
ED EA EgqV0
gi
DAB E
n
NNTkqV
20 ln
W DqN
VW 04
for ND=NA
drift current
dx
dEqn
EqnJ
cn
ndriftn
0
Total net current = 0 (unless externally biased)
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I
V0
forwardreverse
Biasing a diode
n p
Vf
n p
Vr
n p
pn
nn
P
P
TkqV
nL
pL
qAI
eII B
0
/0 ,1
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Hot carriers
resistivity
mobility
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Phonon spectrum1D diatomic chain
Wavevector q
2xTA
1xLA
1xLO
2xTO
Si
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Phys. Rev. 98, 940 (1955)
Bulk Si Seebeck coefficient
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Natural Si(28Si=92%29Si=5%30Si=3%)
enriched Si(28Si=99.9%)
Majumdar, Science (2004)
Thermal conductivity and thermoelectric figure of merit
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Reflected– Same energy (h) and
wavelength ()– Specular: 1’ = 1
Refracted then Absorbed– Snell’s law: n1sin1=n2sin2
– Frequency: 1 = 2 = = /2– Speed of light: n1c1 = n2c2
– Wavelength: n1 1=n2 2
– Intensity: I exp(-d)– Absorption: (h) (h-Eg)1/2
Transmitted 3 = 1
3 = 1, 3 = 1
Scattered– Rayleigh scattering, h = h1
– Raman and Brillouin scattering, h = h1 ħ
– not directional Emitted
– not directional– h Eg
incident
reflected
transmitted
scatteredabsorbed
emitted
1
21’
n1 n2
3
d
iir
ii
ir
ir
irir
ncnc
n
nn
nn
n
nR
iinnn
0
22
22
2
2
0000
22
2
,1
1
1
1
;1; EP
Optical process in semiconductors
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k
kk
kk
k
cv
cvp
cv
p
m
P
m
e
di
2
0
2
22
2
0
2 where
,0
1
ħ
ri
0
GaAs
E1E0
E2
R
0
R
ħE0 E1 E2
(E-E0)1/2 for directbandgap semiconductors
Dielectric Functions of Semiconductors
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Absorptions in SemiconductorsA
bso
rptio
n co
effi
cien
t (cm
-1)
Photon energy (eV)
Wavelength (m)
10-3 10-2 10-1 100 101
100
102
104
106
103 102 101 100 10-1
bandgap
exciton
deeper-bands
free carrier
phonons (lattice vibration)
local impurity vibration
impurity electronic
cyclotron, spin, magnon
core levels
CB
VB+
-
-
+
-
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Fundamentals of photovoltaics
1. “Red” loss
2. Thermalization loss (“blue loss”)
3. Junction loss
4. Contact loss
5. Recombination loss
6. Reflection loss
usable qV
2
345
2
illumination1
6
23
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LED materials
InG
aN
AlG
aAs
AlG
aPA
lGaI
nPG
aAsP
GaP
N
GaN
ZnSe
,
AlN
AlG
aN
GaA
s
