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.