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Ali Shakouri Director, Thermionic Energy Conv. CenterBaskin School of EngineeringUniversity of California Santa Cruz
AVS Thin Film User Group, 8 Nov. 2007
Solid-State Thermionic Energy Conversion for Waste Heat
Recovery
UCSC (Schmidt), Berkeley(Majumdar), Harvard
(Narayanamurti), MIT (Ram),NCSU (Nemanich, Sitar), Purdue (Sands), UCSB
(Bowers, Gossard, Stemmer)Acknowledgement: ONR MURI(Dr. Mihal Gross)
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RejectedEnergy 61%
Total 91.4 quadPopulation: 291M
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AS 11/5/2007Energy Efficiency in Transportation
2/3 of the power in cars is dissipated (heat in the engine and in the catalytic converter)
Terry J. Hendricks, International Conf. on Thermoelectrics; Long Beach, 2002
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AS 11/5/2007
DOE, Energy Information Administration (EAI)
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AS 11/5/2007Seebeck Effect (1821)Seebeck Effect (1821)
SVT
Seebeck:ElectricalConductor
Voltage
Hot Cold
Temperature difference between two junctions can produce a voltage
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AS 11/5/2007
ab
a
I
Q Q
ab a b
QI
Peltier:
Peltier Effect (1834)Peltier Effect (1834)
When the current flows from material (a) into material (b) and then back to material (a), it heats the first junction and cools the second one (or vice versa). Thus, heat is transferred from one junction to the other one.
S TdSdT T
Commercial TE Module• T=72C (no heat load)• Cooling density <10W/cm2
• Efficiency 6-8% of Carnot
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AS 11/5/2007Early Thermoelectricity
• First practical devices USSR during WWII– Tens of thousands built, to power
radios from any available heat source.
• In the 1950s-60s many in the US & USSR felt semiconductor thermoelectrics could replace mechanical engines, much as semiconductor electronics were replacing vacuum tube technology.– Hint: it didn’t happen!
Abram F. Ioffe 1880-1960
Ioffe, A. F. (1957). Semiconductor Thermoelements and Thermoelectric Cooling. London, Infosearch Limited.
Cronin Vining, ZT Services
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AS 11/5/2007Efficiency of Thermoelectric DevicesEfficiency of Thermoelectric Devices
Relative
Efficiency
0.1
0.4
0.3
0.2
ZT1 2 3 4
Commercial TE’s
Typical mechanical systems
Z S2
Z (Seebeck)2 (electrical conductivity)(thermal conductivity)
ab
a
I
Q=+SThI Q=-STcI
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AS 11/5/2007TEs for Telecom Cooling
• Melcor, Marlow and many other TE manufacturers provide coolers specifically designed for Telecom laser-cooling applications
Typical Distributed Feedback Laser:/ T= 0.1 nm/oC
Heat generation kW/cm2
Cronin Vining, ZT Services
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AS 11/5/2007Radioisotope Thermoelectric Generators(Voyager, Galileo, Cassini, …)
• 55 kg, 300 We, ‘only’ 7 % conversion efficiency• But > 1,000,000,000,000 device hours without a single
failure
B-dopedSi0.78Ge0.22
P-dopedSi0.78Ge0.22
B-dopedSi0.63Ge0.36
P-dopedSi0.63Ge0.36
Hot Shoe (Mo-Si)
Cold Shoe
n-type legp-type leg
SiGe unicoupleCronin Vining, ZT Services
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AS 11/5/2007Recent Advances in Thermoelectrics
• Recent advances in nanostructuredthermoelectric materials led to a sudden increase in (ZT)300K > 1
A. Majumdar, Science 303, 777 (2004)
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AS 11/5/2007
PbTe/PbTeSeQuantum DotSuperlattices
ZT=2T.C. Harman, Science, 2002
T=32.2 K, ZT ~2-2.4R. Venkatasubramanian, Nature, 2001
(From M. S. Dresselhaus, Rohsenow Symposium, 2003)
Superlattices/ Quantum Dot Thermoelectrics Harman (2002) and Venkatasubramanian (2001)
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AS 11/5/2007Microrefrigerators on a chip
Nanoscale heat transport and microrefrigerators on a chip; A. Shakouri, Proceedings of IEEE, July 2006
Featured in Nature Science Update, Physics Today, AIP April 2001
1 μm
Hot Electron Cold Electron• Monolithic integration on silicon• Tmax~4C at room temp. (7C at 100C)• Cooling power density >500W/cm2
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AS 11/5/2007Ultra high resolution thermal imaging
• Temperature resolution: 0.006oC• Spatial resolution: submicron
Thermal Image
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AS 11/5/2007
0
1
2
3
4
5
6
7
8
-1
0
1
2
3
4
5
0 2 4 6 8 10 12 14
ZT
(Ebarrier -E
f ) / kB T
Fermi Energy (eV)
Conserved
Non-conserved
Program Manager:Mihal Gross
D. Vashaee., A. Shakouri, Physical Review Letters March 12, 2004
UCSCBerkeleyHarvardMITNCSUPurdueUCSB
Director:A. Shakouri
ZT for metallic nanostructures ZT for metallic nanostructures ThermionicThermionic Energy Conversion Center MURIEnergy Conversion Center MURI
Assume: lattice=1W/mK, mobility ~10 cm2/Vs
Planar Barrier
ZT>5 is possible with metallic structures with hot electron filters.
Metal
Semiconductor
Electrons moving in the material
OR
MetallicNanostructure
Material Parameter (Fermi energy eV)
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AS 11/5/2007Can metal/semiconductor multilayers be grown?Can metal/semiconductor multilayers be grown?
• Minimization of surface energy: If A wets B, B will not wet A.
• Different crystal structures: high defect density; multilayer will not be stable
• Lattice mismatch effect: strain may lead to island growth
int
A
B
AB
B
Challenge: No prior examples of metal/semiconductor multilayers or superlattices with nanoscale periods
Tim Sands (Purdue)
Late 80’s: High speed metal base transistors
Not successful
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AS 11/5/2007High Resolution Microscopy of ErAs Nanoparticles
In,GaAsEr
ErAs particles have the rock salt structure and they are embedded inside InGaAs semiconductor.
ErAs particles have the rock salt structure and they are embedded inside InGaAs semiconductor.
110
001
1nm
D. O. Klenov, D. C. Driscoll, A. C. Gossard, S. Stemmer, Appl. Phys. Lett. 86, 111912 (2005)
HAADFHAADF
AsEr
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AS 11/5/2007
10 nm
HAADF STEMHAADF STEM
Cross-section
[001]
[110]
Particle size distribution for 3% ErAsParticle size distribution for 3% ErAs
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AS 11/5/2007
Plan-view
•Particles are slightly elongated (~ 28%) along the fast [1-10] diffusion direction
•Similar results as for superlattices.
Size Orientation
[1-10]
Radius = 6 nm
Length along long axis
Length in perpendicular direction
Particle sizes and shapes for 3% ErAsParticle sizes and shapes for 3% ErAs
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AS 11/5/2007
0.4 ML 40 nm
0.1 ML 10 nm
In0.53Ga0.47As
Kim et al., Physical Review Letters, 30, 045901 (2006)
In0.53Ga0.47As
0.3 % ErAs
3.0 % ErAs
3.0 % ErAs:In0.53Ga0.28Al0.19As
Thermal Conductivity of ErAs:InThermal Conductivity of ErAs:In0.530.53GaGa0.470.47AsAs
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AS 11/5/2007
Short Wavelength Phonon
Mid/Long Wavelength Phonon
AtomicSubstitution Nanoparticle
Why Thermal Conductivity is Reduced?Why Thermal Conductivity is Reduced?
A. Majumdar (Berkeley)
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AS 11/5/2007
In0.53Ga0.47As
Kim et al., Physical Review Letters, 30, 045901 (2006)
0.3 % ErAs:In0.53Ga0.47As
In0.53Ga0.47AsIn0.53Ga0.47As
0.3 % ErAs:In0.53Ga0.47As
3.0 % ErAs:In0.53Ga0.47As
Meandiameter
Standarddeviation
2.4 nm2.4 nm
1.9 nm1.7 nm
Thermal ConductivityThermal Conductivity
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AS 11/5/2007
ErAs/InGaAs TEM after thermal conductivity measurement
5 nm
ErAs
0.4 ML 40nm ErAs/InGaAs
Material stabilityMaterial stability
images from D. Klenov(UCSB)
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AS 11/5/2007Improve Seebeck using Energy Filters
J. Zide et al., (UCSB, UCSC) Physical Review B, 2006
Theory/ExperimentSeebeck II, (300K) ErAs:InGaAs
/InGaAlAsSuperlattices
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AS 11/5/2007
AlN_low pIate
200 elements of p-ErAs array
Wafer scale module fabrication
AlN_upper plate
200 elements of n-ErAs array
AlN_low plate
AlN_upper plate20 μm elements
400 element generator
Gehong Zeng, John Bowers (UCSB)
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AS 11/5/2007Module Fabrication
400 element ErAs:InGaAlAs thin film generator
Gehong Zeng, John Bowers (UCSB)
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AS 11/5/2007Module Power generation results
140 m/140 m AlN
400 elements (10-20 microns ErAs:InGaAlAs thin films, 120x120 m2)
G. Zeng, J. Bowers, et al. (UCSB, UCSC) Appl. Physics Letters 2006
0
0.5
1
1.5
2
2.5
3
0 20 40 60 80 100 120 140
10 m module20 m module
Out
put P
ower
(W
/cm
2 )
T (K)
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AS 11/5/2007Where does Peltier cooling happen?
InGaAs InGaAsP InGaAs
Heat SinkAnodeBias
HotSourceCathode
Cathodecontactlayer
Anodecontactlayer
Barrier
Mona Zebarjadi, Keivan Esfarjani, Ali Shakouri Phys. Rev. B 74, 195331 (2006)
Distance
SemiconductorContact Contact
Current
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AS 11/5/2007
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.25 0.5 0.75 1 1.25 1.5 1.75length (um)
Ene
rgy
exch
ange
(1E
-9 W
/Cm
^2)
Electron-crystal energy exchange
Peltier Cooling Peltier Heating
Non-equilibriumtransport in the barrier
Energyrelaxationlength in cathode
Energyrelaxationlength in anode
Mona Zebarjadi, K. Esfarjani, A. Shakouri, Phys. Rev. B, 74, 195331 (2006)
Large Seebeck Small Seebeck (contact)
Small Seebeck (contact)
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AS 11/5/2007Nonlinear Peltier Coefficient
Increasingvoltage
200
160
120
80
40 mV
Mona Zebarjadi, Keivan Esfarjani, A. Shakouri –Applied Physics Letter 2007
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AS 11/5/2007Summary• Significant amount of waste heat is generated in cars, power plants, etc.
• Thermoelectric generators can convert heat into electricity without any moving parts
• The efficiency of thermoelectric energy conversion can be improved with the use of nanostructures (increase Seebeck coefficient and electrical conductivity and reduce thermal conductivity)• Potential of semimetallic ErAs nanoparticles in
InGaAlAs semiconductor matrix
Students/postdocsUCSCZhixi Bian, Rajeev Singh, Mona Zebarjadi, Yan Zhang Daryoosh Vashaee,Tammy HumphreyBerkeleyWoochul KimSusanne SingerHarvardKasey RusselMITPeter MayerPurdueVijay Rawat UCSBJosh Zide, Gehong Zeng, J-H Bahk
Acknowledgement: ONR MURI, Packard Foundation
SUMMARY (quantum.soe.ucsc.edu)