1

AS. 26 May 2008

Transient Electrical and Thermal Characterization of InGaAlAs Thin Films

with Embedded ErAs Nanoparticles

Tela Favaloro, Rajeev Singh, James Christofferson, Younes Ezzahri, Zhixi Bian, and Ali ShakouriElectrical Engineering Department, University of California, Santa Cruz, California 95064, USA

Gehong Zeng, Je-Hyeong Bahk, and John E. BowersDepartment of Electrical and Computer Engineering, University of California, Santa Barbara, California

93106, USA

Hong Lu, and Arthur C. GossardMaterials Department, University of California, Santa Barbara, California 93106, US

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AS. 26 May 2008

Outline• High temperature apparatus for cross plane material

characterization• Transient electrical measurements• Thermoreflectance imaging of thermoelectric devices in

cooling and heating modes• Preliminary results

‘Merged’ Thermal Image +500mA, 550K

‘Merged’ Thermal Image -500ma, 550K

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AS. 26 May 2008

Thin Film Material Characterization

TSZT

2

Material Figure of Merit

Established characterization techniques:

• In-plane electrical conductivity and Seebeck (Van der Pauw, sample bars).

• Need non-conducting substrate (difficult at high T). • Substrate transfer: stress issues

• Cross-plane thermal conductivity• 3 (min ~0.5-1m; need electrical isolation between heater and thin film)• Transient thermoreflectance (top 0.1-0.5 microns of the sample, frequency dependent issues)

1

3

2

4

I13 V24

Also possible: Cross-plane determination of material parameters

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AS. 26 May 2008

High Temperature Characterization System

Currently tested to vacuum of 10-6 mbar and temperatures above 800K

High speed measurement stage

Sample mounted for thermal imaging

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AS. 26 May 2008Material System:Semimetal nanoparticles in semiconductor alloy

•Thin film element: 50 m n-InGaAlAs, 0.6% ErAs• Substrate: 125 m AlN • Metal pad: 7 m Au• Mask: Dedicated voltage and current pads

Mask design for cross-plane measurements

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AS. 26 May 2008Cross-Plane Transient Electrical Characterization

0

0.5

1

1.5

2

0 0.1 0.2 0.3 0.4 0.5

300K350K400K450K500K550K600K650K700K

See

beck

Vol

tage

(mV

)

Time (ms)

300K

700K

High speed circuitry enables below 100 nanosecond resolution

300K

750K

500 ns

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AS. 26 May 2008

Extraction of Joule and Peltier Voltages

0

0.5

1

1.5

2

2.5

0 20 40 60 80 100 120 140

Peltier Component of Seebeck Voltage

Vsp 300KVsp 400KVsp 500KVsp 600KVsp 700K

Vsp

(mV

)

Current (mA)

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100 120 140

Joule Component of Seebeck Voltage

Vsj 300KVsj 400KVsj 500KVsj 700KVsj 600K

Vsj

(mV

)

Current (mA)

2110137079870x70 μm2

16901120560120x120 μm2

700K 300K Vsp (V)

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AS. 26 May 2008

Thermoreflectance Imaging

100 150 200 250 300 350 400

50

100

150

200

250

300

350

400-8

-6

-4

-2

0

2

4

6

8

10

100 150 200 250 300 350 400 450

50

100

150

200

250

300

350

400

450

-10

-5

0

5

10

100 150 200 250 300 350 400 450

100

150

200

250

300

350

400

450-6

-4

-2

0

2

4

6

50x50μm2 device in heating mode

50x50μm2 device in cooling mode

50x50μm2 device Subtracted Image for Peltier Cooling

I=+95 mA I = -95 mAT=300K

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AS. 26 May 2008High Temperature Thermoreflectance Imaging

100 200 300 400 500

50

100

150

200

250

300

350

400

450

500-8

-6

-4

-2

0

2

4

6

8

100 200 300 400 500

50

100

150

200

250

300

350

400

450

500 -4

-3

-2

-1

0

1

2

3

4

100 200 300 400 500

50

100

150

200

250

300

350

400

450

500-5

-4

-3

-2

-1

0

1

2

3

4

I =+95mA I=- 95mAT=700K

50x50μm2 device in heating mode

50x50μm2 device in cooling mode

50x50μm2 device Subtracted image for Peltier Cooling

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AS. 26 May 2008

Total Cooling Density Varies with Device Size

300 350 400 450

160

180

200

220

240

260

280

300

320

340

360 -6

-4

-2

0

2

4

6

150 200 250 300 350 400

150

200

250

300

350

400 -6

-4

-2

0

2

4

6

100 150 200 250 300 350 400

100

150

200

250

300

350

400

-8

-6

-4

-2

0

2

4

6

8

50x50μm2 with 95mA excitation current

100x100μm2 with 140mA excitation current

150x150μm2 with 150mA excitation current

Current injection nonuniformity and current spreading within the sample result in decreased ΔT in larger samples

ΔT=-3.995 ΔT=-2.067 ΔT=-1.655

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AS. 26 May 2008

Results and ConclusionsDetermination of Seebeck Coefficient for 70x70μm2 Sample:

Measured change in temperature after subtraction of Joule heating at 100mA excitation:

160

180

200

220

240

260

280

300

320

200 300 400 500 600 700 800 900

Comparison of Cross-Plane Seebeck with Independant In-Plane Measurement

Seeb

eck

Coe

ffici

ent (

uV)

Ambient Temperature (K)-6.656-5.018-4.215ΔT (K)21101370798Vsp (V)700K 300K

SP

SP

TVS