pyroelectric and piezoelectric properties of gan-based ... · pdf filepyroelectric and...

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[email protected] # 20

SDM-2, ©Michael Shur 1999-2009

Pyroelectric and Piezoelectric Properties of GaN-based Materials and Devices

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Outline

Pyroelectric effect and pyroelectric sensorsPiezoelectric properties and piezoelectric

sensorsPolarization doping in GaN-based

heterostructuresStrain energy band engineeringConclusions

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It is complex!

“The Universe is full of magical things patiently waiting for our wits to grow sharper”

Eden Phillpotts

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Wide Gap SemiconductorsEnabling Technology for Piezo-electronics

Zinc blende structureNo PE or SP effect in <100 > directionPE coefficient <111> ~0.15 C/m2

No PE/SP ‘doping’ reported

• Wurtzite structure• c-axis growth direction • PE coeficient in c-direction ~1

C/m2

• PE/SP ‘doping’ demonstrated

GaAs GaN/AlN

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Ga and N faces

G a ll i u m f a ce

Ni tr o g e n f a c e

[000 1][0001]

After Hellman, E. S., The Polarity of GaN: a Critical Review. MRS Internet J. Nitride Semicond. Res. 3, 11(1998)

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Polarization sign

GaN

GaN

GaN

AlGaN

AlGaN

AlGaN

Relaxed

Relaxed

TensileStrain

CompressiveStrain

Relaxed

Relaxed

GaN

GaN

GaN

AlGaN

AlGaN

AlGaN

Psp

Psp

Psp

Psp

Ppe

Ppe

Psp

Psp

Ppe

Ppe

Psp

Psp

PspPsp

+σ

+σ

-σ +σ

-σ

-σ

[0001] [0001]

Ga face N face

After O. Ambacher et al. J.Appl. Phys. 85, 3222 (1999)

2D electrons

2D holes

2D holes

2D electrons

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Spontaneous polarization

For comparison, in BaTiO3, Ps = 0.25 C/m2

-0.045-0.057-0.032-0.029-0.081Spontaneous polarization(C/m2)

BeOZnOInNGaNAlNAfter F. Bernardini et al. Phys Rev. 56, 10024(1997)

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Equivalent circuit of pyroelectric sensor

IpPyroelectr icm aterial

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Primary and secondary pyroelectric effects

b

-100-50

050

-4 0 4 8 12 16 20

Time, s

-1

0

1

2

3

-4 0 4 8 12 16 20

0

-40

-80

a

c

-0.2

0.1

0.4

0.7

1

0 2 4 6 8 10 12Time, s

0

50

1000 2 4 6 8 10 120 2 4 6 8 10 12

50

0

Slow heat transferFast heat transfer

(after A. D. Bykhovski, V. V. Kaminski, M. S. Shur, Q. C. Chen, and M. A. Khan "Pyroelectricity in gallium nitride thin films", Appl. Phys. Lett., 69, 3254 (1996)).

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Pyroelectric voltage for primarypyroelectric effect (changing flux magnitude)

From A. D. Bykhovski, V. V. Kaminski, M. S. Shur, Q. C. Chen, and M. A. Khan "Pyroelectricity in gallium nitride thin films", Appl. Phys. Lett., 69, 3254 (1996)

-1

0

1

2

3

4

5

6

7

8

9

-0.5 0 0.5 1 1.5 2 2.5 3Time (s)

Heat Flux Counter!

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Pyroelectric voltage for primarypyroelectric effect (changing flux magnitude

and direction)

0 20

0

0.4 (c )

0

20

(a)

-20

0

(b)

Bat

h te

mp

erat

ure

(oC

)H

eat

flux

(a

.u)

Tim e (s )10 30 40

-0.4Vo

ltage

(m

V)

20

40


Heat Flux Counter!

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Two time constants for primarypyroelectric effect

b

-100-50

050

-4 0 4 8 12 16 20

Time, s

-1

0

1

2

3

-4 0 4 8 12 16 20

0

-40

-80

a

c

τT reflects the rate of the sample cooling due to free convection

τs reflects the pyroelectric charge relaxation.


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Primary pyroelectric effect at 300 oC(High Temperature Operation!)

0

0

4

8

b .

0

a .Ga N

T(o

C)

300

200

100

12

Vol

tag

e (m

V)

10 20 30 40

Tim e (s )

Constant temperature of “cold”contact (94 oC) is shown by dotted line.

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Pyroelectric coefficients

From M. S. Shur, A. D. Bykhovski , R. Gaska, and M. A. Khan, GaN-based Pyroelectronics and Piezoelectronics,to be published

LiTaO3

0

2

4

6

8

10

12

14

0

2

4

6

8

10

12

14

PbTiO3PZTPVDFBaTiO2TGSGaN

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Curie temperature

0

500

1000

1500

2000

0

500

1000

1500

2000

LiTaO3 PbTiO3PZTPVDFBaTiO2TGSGaN

From M. S. Shur, A. D. Bykhovski, R. Gaska, and A. Khan, GaN-based Pyroelectronics and Piezoelectronics,in Handbook of Thin Film Devices, Volume 1: Hetero-structures for High Performance Devices, Edited by Colin E.C. Wood, Handbook edited by Maurice H. Francombe, pp. 299-339, Academic Press, San Diego, 2000

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Piezoelectric Properties of GaN

.

1.00.80.60.40.2-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Ionicity

ZnSe

ZnTe CdTeInPInAs

AlSb InSb

GaAsAlAs

GaSb

GaN

0

e 14

( C/ m

2 )

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Piezoelectric constantselm (C/m2) e33 e31 e15 e14GaN(electromechanicalcoefficients)

1 -0.36 -0.3

GaN(mobility)

0.44 -0.22 -0.22 0.375

GaN (fromoptical phonons)

0.65 -0.33 -0.33 0.56

GaN (ab initio) 0.73 -0.49InN (from opticalphonons)

0.43 -0.22 -0.22 0.37

InN (ab initio) 0.97 -0.57AlN (surfaceacoustic waves)

1.55 -0.58 -0.48

AlN (ab initio) 1.46 -0.60SiC 0.2 0.08ZnO 1.32 -0.57 -0.48GaAs -0.185 0.093 0.093 -0.16

From M. S. Shur, A. D. Bykhovski, R. Gaska, and A. Khan, GaN-based Pyroelectronics and Piezoelectronics,in Handbook of Thin Film Devices, Volume 1: Hetero-structures for High Performance Devices, Edited by Colin E.C. Wood, Handbook edited by Maurice H. Francombe, pp. 299-339, Academic Press, San Diego, 2000

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How Piezoelectric constants are determined?

Electromechanical coefficients (difficult)Optical experiments (indirect)Estimate from transport measurements (very

indirect)

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Strain from the lattice mismatch

uxx = (aGaN -aAlGaN)/aGaNStrain with metal - to be analyzed?Thermal expansion - important for sapphire

substrate, relatively unimportant for AlGaN/GaN interfaces

Ppe = 2 uxx (e31-e33 C13/C33)

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Effect of Strain on Dislocation-Free Growth

Critical thickness as a function of Al mole fraction in AlxGa1-xN/GaN: superlattice (solid line), SIS structure (dashed line).

From A. D. Bykhovski, B. L. Gelmont, and M. S. Shur, J. Appl. Phys. 81 (9), 6332-6338 (1997)

0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1

Al Mole Fraction

Thickness, nm

Can it be exceeded?

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• High Al- Heterostructures• Origin of Doping?

i-GaN

Al0.25Ga0.75N

AlN

SiC100 200 300 400 500 600

1,000

2,000

3,000

300K

77K

Hal

l Mob

ility

(cm

2 /Vs)

AlGaN Thickness (A)

Critical Thickness dcr ~ 30 nm

Effect of Critical Thickness on Electron Mobility

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Model Assumptions

Isotropic approximationAveraged (over the layers) elastic constantsIdeal crystal (except, of course, for misfit

dislocations)The critical thickness is found by minimizing

the deformation energy with respect to the misfit dislocation density

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SIS sensor

Piezoelectric sensorsPyroelectric sensors

Sapphire

n- GaNAlNn- GaN

Contacts

After R. Gaska, J. Yang, A. D. Bykhovski, M. S. Shur, V. V. Kaminski, S. M. Soloviev,

Appl. Phys. Lett. 71(26), 3817 (1997)

c

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SIS structure and Band Diagram

n - GaN 0.4 μm

AlN 30 Å - 100 Å

n - GaN 1.0 μm

i - GaN 1.0 μm

AlN Buffer

Sapphire

Top ContactBottomContact

GaN n

F

(1) (2) (3)

GaN n

Ef

Ev

Ec

L

AlNu

B A B A B A

From A. Bykhovski, B. Gelmont, M. S. Shur, and A. Khan. Strain and Charge Distribution in GaN-AlN-GaN SIS Structure,in: Proceedings of International Conference on Silicon Carbide and Related Materials-1993, Washington DC,

Institute of Physics Publishing, Institute of Physics Conference Series Number 137, 1994, p. 691- 694.

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SIS capacitance

From A. Bykhovski, B. Gelmont, and M. S. Shur, J. Appl. Phys. 74(11), 6734 (1993).

0

1

2

3

4

5

6

-2 -1 0 1 2 3Voltage (V)

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Resistance of SIS structure with 50 nm top GaN layer versus compressive strain.

44.4

44.5

44.6

44.7

44.8

44.9

45

45.1

45.2

45.3

0 0.5 1 1.5 2 2.5 3

After R. Gaska, J. Yang, A. D. Bykhovski, M. S. Shur, V. V. Kaminski, S. M. Soloviev,

Appl. Phys. Lett. 71(26), 3817 (1997)

Twice as largeas in SiC

Short range superlatticeis four timeslarger than inSiC

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Possible domain structure

After A. D. Bykhovski, V. V. Kaminskii, M. S. Shur, Q. C. Chen, and M. Asif Khan, Piezoresistive Effect in Wurtzite n-type GaN, Appl. Phys. Lett., 68 (6), pp. 818-819 (1996)

N

GaGa

GaSurface

N

GaGa

N N

GaGa

NSurface

NGaGaN

Surface

NGaGaN

N

N N

Ga

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F i g . 1 E p i l a y e r d e s i g n o f [ ( A l N ) m - ( G a N ) n ] p S R S L s t r u c t u r e .T h e c o n s t a n t c u r r e n t w a s m a i n t a i n e d b y o h m i c c o n t a c t s 1 , 4a n d s a m p l e r e s i s t a n c e w a s e s t i m a t e d b y m e a s u r i n g v o l t a g ed r o p b e t w e e n c o n t a c t s 2 a n d 3 . A r r o w s s h o w t h e d i r e c t i o n so f t h e s t r a i n c o m p o n e n t , u x x

S a p p h i r e

2 μ m G a N

3 0 0 n m

2 5 n m G a N

[ ( A l N ) m - ( G a N n ) ] p

1 2 3 4

( 0 0 0 1 )

xu x x u x x

Short Range Superlattices

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Superlattice Band Diagram

y

A A A A AB B B BBeffec tiveband gap

(0001)En

erg

y (e

V)

After A. D. Bykhovski, B. L. Gelmont, and M. S. Shur, Elastic Strain Relaxation in GaN-AlN, GaN-AlGaN, and GaN-InGaN Superlattices, J. Appl. Phys. Vol. 81, No. 9, pp. 6332, May (1997

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0.0 0.5 1.0 1.5 2.0 2.5 3.0

0

5

10

15

20

25

3

21

δR/R

(10-3

)

Strain (10-4 )

Fig. 2 Relative change in resistance under applied strain. (o) - correspond to [(AlN)6-(GaN)3]150 SRSL ; (Δ) - [(AlN)3-(GaN)8]150 SRSL; solid line 1 shows dependence measured for GaN-AlN-GaN SIS 1; dashed line 2 - SiC p-n junction 1 ; 3 - GaAs 2. The GF for the measured samples was in the 30 to 90 range.The larger GF (higher sensitivity to strain) was measured in SRSLs with higher Al content.

1 J. S. Shor, L. Bemis, and A. D. Kurtz, IEEE Trans. Electron Dev. , 41 (5), 661 (1994).2 A. Sagar, Phys. Rev., 112, 1533 (1958); 117, 101 (1960).

Resistance change in SRSL

SRSL

SiCGaN

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0.0 0.5 1.0 1.5 2.0 2.5 3.00

20

40

60

80

100

2

1

Gau

ge F

acto

r

Voltage (mV)

Gauge factors for [(AlN)m-(GaN)n]p SRSL structures and different biases. (o) and line 1 correspond to [(AlN)6-(GaN)3]150 SRSL; (Δ) and line 2 - [(AlN)3-(GaN)8]150 SRSL. At each voltage, a number of measurements were taken for different strains in 0.5x10-4 – 2.4x10-4 range.

Gauge Factor in SRSL

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Static Gauge factors (GF)(measured under longitudinal mechanical deformation)

GaNn-type GF=10

p-type GF > 200

GaN/AlN/GaN SapphireGF = 50

AlN/GaN Short Range Superlattices

GF = 30-80

AlGaN/GaN HeterostructuresGF = 10-15

0 1 2 3 4 50 .0 0

0 .0 2

0 .0 4

0 .0 6

0 .0 8

0 .1 0

0 .1 2

p -G a N

S iS iC

G a N /A lN /G a NδR/R

S tra in , 1 0 -4

High Temperature p-GaN Pressure Sensor

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Piezoelectric effect in doped and undoped channel

GaN/AlGaN HFETs.

2

-20 20 40

0

Ener

gy (e

V)

Distance (nm)

Undoped

Nd = 5x1017 cm-3 1

After M. S. Shur, GaN and related materials for high power applications, Mat. Res. Soc. Proc. Vol. 483, pp. 15-26 (1998) M. S. Shur, GaN and related materials for high power applications, Mat. Res. Soc. Proc. Vol. 483, pp. 15-26 (1998)

Up to 4x1013 cm-2 inGaNversus 2x1012 cm-2

in GaAs

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Piezoelectric effect (opposite polarity)

-4

0En

ergy

(eV)

Distance (nm)

-20

-2

20 40

After M. S. Shur, GaN and related materials for high power applications, Mat. Res. Soc. Proc. Vol. 483, pp. 15-26 (1998) M. S. Shur, GaN and related materials for high power applications, Mat. Res. Soc. Proc. Vol. 483, pp. 15-26 (1998)

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C-V of AlGaN/GaN heterostructuresshow the presence of residual strain

••••••••

•••••••••••••

••••••••••••••••••••••••••••••

••••••••••••••••••••••••••

0

0.002

0.004

0.006

0.008

0.01

-16 -12 -8 -4 0Voltage, V

10 nm (100% strained)

20 nm (100% strained)

40 nm (60%)60 nm (30%)100 nm (0%)

From A. D. Bykhovski, R. Gaska, and M. S. Shur, Appl. Phys. Lett. 73 (24) (1998).

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Piezoelectric and Pyroelectric Doping in AlGaN/GaN

A l M o la r F r a c t io n

0

1

2

3

4

5

6

0 0 .2 0 .4 0 .6 0 .8 1

State-of-the-art

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Maximum Electron Sheet Density

0

5

10

15

20

25

30

35

GaA

s/A

l Ga A

s

InG

a As/

A lG

a As

Ga N

/Al G

aN

Ga N

/AlIn

GaN

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Electronic island at the surface of semiconductor grain in pyroelectric matrix

(MQDs -Moveable Quantum Dots)

Control by external field – Zero dimensional Field Effect (ZFE)

Po

Semiconductor

Electronic island

PyroelectricPo

Semiconductor

Electronic inversion island

Pyroelectric

Hole inversion island

Inversion electron and hole islands at the surface of pyroelectric grain in semiconductor matrix

After V. Kachorovskiy and M. S. Shur, APL, March 29 (2004)

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Terahertz oscillations

MOVABLE QUANTUM DOTS (MQD)

CAN SWITCH OR SHIFT FREQUENCY BY EXTERNAL FIELD OR BY LIGHT

1 THz to 30 THz

2D island might oscillate as a whole over grain surface. The oscillations can be exited by AC field perpendicular to Po

00

4( 2 )p

ePmR

=+

πωε ε

Oscillation frequency is of the order of a terahertz

0 2~ω π/

Oscillation frequency

After V. Kachorovskiy and M. S. Shur, APL, March 29 (2004)

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Key references

M. S. Shur, A. D. Bykhovski, R. Gaska, and A. Khan, GaN-based Pyroelectronics and Piezoelectronics, in Handbook of Thin Film Devices, Volume 1: Hetero-structures for High Performance Devices, Edited by Colin E.C. Wood, Handbook edited by Maurice H. Francombe, pp. 299-339, Academic Press, San Diego, 2000

Piezoelectric effect in AlGaN/GaN HFETs-P. M. Asbeck, E. T. Yu, S. S. Lau, G. J. Sullivan, J. Van Hove, and J. M. Redwing, Electron. Lett. 33, 1230 (1997)

Piezoelectric constants and spontaneous polarization in III-N ab-initio-F. Bernardini and V. Fiorentini, Phys. Rev. B 56(16), 10024 (1997);

Predicted red shift in GaN-based QWs- J. Wang, J. B. Jeon, Yu. M. Sirenko, and K. W. Kim, Photonics Technol. Lett. 9 (6), 728 (1997).

Observed red and blue shift in InGaN/GaN QWs- A. Hangleiter, Jin Seo Im, H. Kollmer, S. Heppel, J. Off, F. Scholz, MRS Internet J. Nitride Semicond. Res. 3, 15 (1998).

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Conclusions

•Pyroelectric properties of GaN are comparable to those of the pyroelectric ceramics such as PZT or BaTiO3•Both primary and secondary pyroelectric effects have been observed in GaN based structures. •piezoresistive effect in GaN/AlN multilayer structures up to 4 times larger than in SiC. •Role of spontaneous polarization, the role of surface and interface states, and of the inversion domains must be ascertained•Polarization doping plays dominant role in AlGaInN/GaN HEMTs

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