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Zhixi BianSchool of EngineeringUniversity of California, Santa Cruzzxbian@soe.ucsc.edu
ElectronicsQuantum
Group
ElectronicsQuantum
Group
Low dimensional and nanostructured InGaAlAs materials for thermoelectric energy conversion
Collaborators
R. Singh, M. Zebarjadi, Ali Shakouri (UC Santa Cruz)
J. M.O. Zide, A. C. Gossard (UC Santa Barbara, Delaware)
S. Singer, W. Kim, A. Majumdar (UC Berkeley, Yonsei University)
G. Zeng, J-H. Bahk, J.E. Bowers (UC Santa Barbara)
Outline
Thermoelectric effects Low dimensional materials:
superlattices Nanoparticle materials Summary
Thermoelectric Effects
S V
TSeebeck:
ab
V
T1T2
a
ab a b Q
IPeltier:
a
b
a
I
Q Q
STab
Application: microelectronics cooling
Steve Kang et al. Electrothermal analysis of VLSI Systems, Kluwer 2000
T=20C
Mean-time-to-failure due to electromigration increase x5
110C
108C90C80C
1 cm
On chip temperature contour
Dependence of mean time to failure on temperature
Application: optoelectronics cooling
Typical DFB Laser: /T= 0.1 nm/oC, Heat
generation kW/cm2
Scheerer et al., Siemens AG, Elec. Lett. 35, (20, Sept. 1999)
Fiber Optic Link: 3200 Gbit/s80 Lasers, 40 Gb/s per laser0.8nm channel spacing
Wavelength Division Multiplexing
0 1 0 1 1 00 1 0 1 1 0
~ 100 km~ 100 km ~ 100 km
~ 0.4 nm ~ 0.8 nm
• Optoelectronic device used in high-speed, multi wavelength fiber optic communication systems generate kW/cm2 and they need temperature stabilization.
Challenge: integrated optoelectronics
Electroabsorption modulator
Waveguide Ridge
20um
V=2.7V V=0V
Light
Out
Front Mirror Gain Phase
Rear Mirror
SG -DBR
Laser
Amplifier
EA Modulator
MQW active regions Q waveguide Sampled Grating
Zhixi Bian, et al., Appl. Phys. Lett. 27, 3605 (2003)
Bias (V)
Tem
pera
ture
Cha
nge
(C)
Standard Thermal Design
+160C
0
50
100
150
200
0 1 2 3 4 5 6
Application: energy conversionPossible ApplicationsPossible Applications
• Electric power generator with no moving part• Electric Ships (Seapower 21)• Waste heat recovery (cars, power plants, …)• Microscale power sources
Thermoelectric figure-of-merit ZT
Z S2
Z (Seebeck)2 (electrical conductivity)
(thermal conductivity)
Maximum Cooling:
2max 2
1)( CCH ZTTT R
TSQ c
2
22
max
Terry M. Tritt et al., MRS Bulletin March 2006
;2
1 2 TKRIISTQ C
Net Cooling:
Peltier Cooling
Joule Heating
Heat Conduction
Peltier cooling: microscopic picture
Density of States
E
Ef
d(E)
E
Differential Conductivity
ST
f(E)
E
ETE
EfEEvEeE xd
022
dEE
dEEEdEEEE
eTK
F
Fe
E)(σ
)()(σ)(σ
1
d
2
d2d2
kk
f
d
FdEE
dEE
dEEEE
eTS
)(
)()(1
dEEd )(
Optimal doping
J. Snyder (2003) http://www.its.caltech.edu/~jsnyder/thermoelectrics/science_page.htm
For almost all materials, if doping is increased, electrical conductivity increases but Seebeck coefficient is reduced.
Low dimensional materials (in-plane)
Dresselhaus M S et al, Microscale Thermophysical Engineering 3, 89 (1999).
2D
1D
Density-of-States
Energy
Bi
[100] PbTe, QWell SL
[001] PbTe, QWire SL
D. A. Broido, T. L. Reinecke, Phys. Rev. B 64, 045324 (2001)
(1) Full band structure(2) Inelastic scattering
Thermionic emission and MQW SL (cross-plane)
Energy Hot electron
Cold electron
Cathode Barrier Anode
Thermionic: If barrier is thin or nanostructured (< electron energy relaxation length) => Can not define barrier Seebeck coef. independent of contact layers (ballistic, non-linear transport)
Material 1 Material 2 Single Barrier
Material 1
Non-planar barrier
Zhixi Bian et al., Appl. Phys. Lett. 88,
012102 (2006)
BarrierEmitter Collector
Peltier power profile
Mona Zebarjadi et al., Phys. Rev. B 74,
195331 (2006)
Multilayers and MQW superlattices
G. Chen, Phys. Rev. B 57, 14 958 (1998). M. V. Simkin and G. D. Mahan, Phys. Rev. Lett. 84, 927 (2000). R. Venkatasubramanian, E. Siivola, T. Colpitts, and B. O'Quinn, Nature 413, 597 (2001).
Reduced parasitic (contact) effects Reduced thermal conductivity
Optimize electronic thermal conductivityZ. Bian, et al., Phys. Rev. B 76, 205311 (2007)
Material 1 Material 2 Superlattice
Material 1
Interface scattering and coherence
R. Venkatasubramanian, Phys. Rev. B 61, 3091 (2000)
~ phonon wavelength
2.5~25nm
Bi2Te3/Sb2Te3 superlattices
T=32.2 K, ZT ~2-2.4R. Venkatasubramanian, Nature 413, 597 (2001).
Power Factor (W/cmK2) 40 50.9Thermal Conductivity (W/mK) 0.5 1.26
Superlattices Bulk
InGaAs
10-5
0.0001
0.001
0.01
0.1
AlP
AlS
bG
aA
sG
aN
Ga
PG
aS
bH
gC
dT
e .
2H
gC
dT
e .
3H
gC
dT
e .
4H
gC
dT
e .
5H
gC
dT
e .
6H
gC
dT
e .
7In
As
InG
aA
s .
53
InG
aA
sP
.77
,.5 InN
InP
InS
bG
e (
n)
Ge
(p
)S
i (n
)S
i (p
)S
iGe
.7
(n
)S
iGe
.7
(p
)B
iTe
(n
c)
(n)
BiT
e (
n c
) (p
)
Mobility
Thermal conductivity m Electron effective mass
m1.5/
Material Optimization for Heterostructure Integrated Thermionic Coolers, Ali Shakouri, Chris Labounty, Invited Paper, International Conference on Thermoelectrics, pp. 35-39, Baltimore, MD, August 1999.
ErAs/InGaAs-InGaAlAs for energy conversion
The barrier height can be adjusted by Al composition
ErAs particles reduce the thermal conductivity
(InGaAs) 0.6(InAlAs) 0.4 digital alloy(n-InGaAs) embedded with 0.3% Er nanoparticles randomly distributed (2×1018 cm-3)+Si dopants [(0-2-4-8)× 1018 cm-3]
×70
n-InP substrate
50nm 5E18 n-InGaAs
20nm n-InGaAs
10nm InGaAlAs
20nm n-InGaAs Cap layer
Seebeck coefficients and modeling
Zhixi Bian, et al., Phys. Rev. B 76, 205311 (2007)
Oscillation with doping
The thermoelectric power factor and electronic thermal conductivity can be optimized with doping and SL thickness
Phonon scattering by particles
Bulk Alloy Bulk Alloy + Nanoparticles
After W. Kim
Reduced thermal conductivity
Thermal conductivity is reduced by interface and nanoparticle scattering of phonons
W. Kim et al., Appl. Phys. Lett. 88, 242107 (2006)
Energy conversion module
AlN
InP
Flip chip bonding
AlN
Substrate remove
InP
AlN
Contact metal deposition on top of superlattice G. Zeng et al, Appl. Phys. Lett. 88,
113502 (2006)
Nanostructured materials
PbTe/PbTeSe Quantum Dot Superlattices
0D confinement ???? Particle scattering of phonons/ electrons
Ternary: ZT=1.3-1.6Quaternary: ZT=2T=43.7 K, Bulk T=30.8 KT.C. Harman et al., Science 297, 2229(2002)
Power Factor (W/cmK2) 25.5 28Thermal Conductivity (W/mK) 0.5 2.0
QD Bulk PbTe
ErAs/InGaAlAs -- thermal
0.4 ML 40 nm
0.1 ML 10 nm
In0.53Ga0.47As
W. Kim et al., Phys. Rev. Lett. 30, 045901 (2006)
In0.53Ga0.47As
0.3 % ErAs
3.0 % ErAs
3.0 % ErAs:In0.53Ga0.28Al0.19As
ErAs/InGaAlAs -- electrical ErAs nanoparticles might dope the holding materials
more efficiently Free carrier concentration can be adjusted by particle
size, and the holding material composition
D. Driscoll (UCSB), PhD Thesis
-0.1
-0.05
0
0.05
0.1
0 0.5 1 1.5
Fer
mi l
evel
(eV
)
ErAs Deposition (ML)
Conduction band edge
ErAs/InGaAs
(InGaAs)1-x(InAlAs)x—electrical conductivity
By changing the composition of Al, the carrier concentration can be adjusted
The carrier concentration also increases with temperature. This self-adaptability might offer an optimal material for a large temperature range
200 300 400 500 600 700 800 90010
16
1017
1018
1019
1020
Temperature [K]
Car
rier c
once
ntra
tion
[cm
-3]
20% InAlAs
40% InAlAs
60% InAlAs
80% InAlAs
InP substrate only(multiplied by thickness ratio)
Measured at JPL with help from T. Caillat Substrate contribution is negligible <600K
20% Al
200
250
300
350
400
450
500
300 350 400 450 500 550 600
Ele
ctric
al C
on
duct
ivity
(/o
hm
-cm
)
Temperature (K)
(InGaAs)1-x(InAlAs)x- Seebeck coefficient
The Seebeck coefficient still increases with temperature, even the carrier concentration becomes larger
180
200
220
240
260
280
300
320
340
300 350 400 450 500 550 600
Se
ebe
ck c
oef
ficie
nt (
µV
/K)
Temperature (K)
20% Al
Average temperature stage300K to >800K
Cold side
Hot side
S
P
Electrical feedthrough
Vacuum feedthrough
Radiation shielding
Ceramic thermal
insulators
Measurement Probe
Sample
Vacuum chamber
Viewport
Measured at UCSC
(InGaAs)1-x(InAlAs)x—thermal conductivity
2
2.2
2.4
2.6
2.8
3
3.2
300 350 400 450 500 550 600
Th
erm
al c
on
duct
ivity
(W
/m-K
)
Temperature (K)
Measured at UC Berkeley
20% AlI(ω)
V(ω), V(3ω)
Power factor and ZT
Thermoelectric power factor increases and thermal conductivity decreases with the increase of temperature
A usually poor thermoelectric material achieves ZT ~1 at 600 K, when ErAs nanoparticles are embedded
0
0.001
0.002
0.003
0.004
0.005
0
0.2
0.4
0.6
0.8
1
1.2
300 350 400 450 500 550 600
Power factor
ZT
Th
erm
oele
ctric
pow
er
fact
or
(W/m
-K2 )
ZT
Temperature (K)
20% Al
Where we are
ErAs:InGaAlAs
Power generation module
Made by flip-chip bonding and wafer transfer at UCSB
2.5 W/cm2 power output is demonstrated with the most recent module
0.01
0.1
1
10
1 10 100 1000O
utp
ut
po
wer
(W
/cm
2)
External resistor load ()
20m generator modules
10m generator modules
Some modeling---scattering
Three major electron scattering mechanisms
0 0.05 0.1 0.15 0.2 0.25 0.30
2
4
6
8
10
12
14
16x 10
12
E (eV)
Sca
tterin
g r
ate
(/s
)
Ef=0.043eV
electron per ErAsparticle is 2.12
ErAs particlescatteringpolar optical
phonon scattering
impurityscattering
pr
0V
*
2
2m
kE
2k
1k
Electron energy
By UCSB and UCSC
Some modeling---fitting
0
500
1000
1500
2000
300 400 500 600 700 800
total measurementsubstrate filmsubstrate+filmsubstrate measurement
Ele
ctric
al c
ond
uctiv
ity (
/oh
m-c
m)
T (K)
500
1000
1500
2000
300 400 500 600 700 800
measurement-SBmeasurement-SC substratefilmsubstrate+film
Se
ebe
ck c
oef
ficie
nct
(µ
V/K
)
T (K)
Fitting with experimental results with two parameters in nanoparticle scattering
20% Al
Some modeling---prediction
To improve the performance at ~400 K, smaller particle size might help
0
0.001
0.002
0.003
0.004
0.005
0.006
1017 1018 1019
rm 2.4, rv 0.5rm 1.2, rv 0.95 rm 1.2, rv 0.5rm 1.2, rv 0.2rm 0.6, rv 0.5rm 0.6, rv 0.2
Po
wer
fact
or
(W/m
-K2 )
Co-doping (/cm3)
Current sample
After W. Kim, UC Berkeley
Improved thermoelectric power factor
Poudel, B., et al. (2008). "High-ThermoelectricPerformance of Nanostructured Bismuth Antimony Telluride Bulk Alloys." Science: 1156446
38
Power Factor (S2σT): 0.3% Er / control
0.3% Er:InGaAlAs
Control (2E18 Si, no Er)
Summary Thermoelectric materials have applications in
thermal management and thermal-to-electrical energy conversion.
Low dimensional and nano structures may improve the thermoelectric performance.
We have made superlattices and nanoparticle materials using conventional semiconductor materials.
A power generation density (2.5 W/cm2) have been achieved.
Similar material systems and optimal potential barrier, particle size and concentration may offer increased thermoelectric power factor besides reduced thermal conductivity, in turn, higher thermal to electrical energy conversion efficiency.
More accurate modeling of the thermoelectric effects of nanoparticles is ongoing.
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