High Voltage GaN Devices for Photovoltaics and High Frequency … · 2011. 8. 3. · High Voltage GaN Devices for Photovoltaics and High Frequency Switched Power Supplies H. Rusty

HIPER Lab

Harris Integrative Photonics and Electronics Research Laboratory

High Voltage GaN Devices for

Photovoltaics and High

Frequency Switched Power

Supplies

H. Rusty Harris

Texas A&M University

Depts. Of Physics and ECE

SLAC Advanced Instrumentation Seminars July 27, 2011

Outline

• Motivation

• GaN design for 5kV

• Additional device and integration needs

• Summary

http://www.tamu.edu/http://engineering.tamu.edu/

Students and Collaborators

• PhD Students

– Iman Rezanejhad

– Derek Johnson

– Mary Coan

– Jung Hwan Woo

• Collaborators

– Mark Holtz and Sergey Nikishin – Texas Tech

University

– Eddie Piner – Texas State University

http://www.tamu.edu/http://engineering.tamu.edu/

Outline

• Motivation

• GaN design for 5kV

• Additional device and integration needs

• Summary

http://www.tamu.edu/http://engineering.tamu.edu/

Area Needs for advanced HV

switches

Photovoltaics

High Voltage drives RF and microwave communications

http://www.tamu.edu/http://engineering.tamu.edu/

• We’re getting there

PV Progress

http://www.tamu.edu/http://engineering.tamu.edu/http://upload.wikimedia.org/wikipedia/commons/e/ed/PVeff(rev110408U).jpg

• Higher voltage in the

arrays will reduce

resistive losses

– Residential: 600V

– Commercial: 1000V

Switched power supplies in PV

http://www.tamu.edu/http://engineering.tamu.edu/

E

E

E

E

A

B

C

D

A

B

C

D

Higher Voltage requires more

components

Minority carriers in large drift regions

cause reverse current after switching

http://www.tamu.edu/http://engineering.tamu.edu/

• Clear Advantage in

terms of scaling for MV

applications

6 MW LV (690 V) full-power converter system for

wind turbine

6 MW MV (3300 V) full-power converter for wind turbine

Medium Voltage energy

advantage

Microwave Switches- RF Switches

http://www.tamu.edu/http://engineering.tamu.edu/http://www.tamu.edu/http://engineering.tamu.edu/

Outline

• Motivation

• GaN design for 5kV

• Additional device and integration needs

• Summary

http://www.tamu.edu/http://engineering.tamu.edu/

0.1

1

10

100

100 1000 10000

On

-Sta

te R

esis

tan

ce (

milli O

hm

s.C

m^

2)

Breakdown Voltage (V)

GaN SiC

US

SankeMatsushit

Furukawa

Toshiba

Denso CELEGY

Siemens

Purdue

CREE SICE

D

Siemens Mitsubishi SICE

D

Kansai Power

Electronics & CREE Si-

Limit

SiC-

Limit

GaN-

Limit

Huang

[26]

[27] [28]

[29]

Current Status of Alternate

switching technology

http://www.tamu.edu/http://engineering.tamu.edu/

• AlGaN/GaN forms a high

density 2D Electron Gas

– Low on state resistance!

• We can grow high quality

GaN on a Si platform

– Up to 300mm possible!

Benefits of GaN HEMT in HV

applications

http://www.tamu.edu/http://engineering.tamu.edu/

Our Goal

• Use the HEMT architecture and all its benefits, but

still retain high voltage blocking characteristics

http://www.tamu.edu/http://engineering.tamu.edu/

Spontaneous and Piezoelectric

Polarizations

jijp

i eP

]0,0,0,,,[ 321

^

31

^

0

0

e

e

31

0

0

e 33

0

0

e 0

0

14e

0

0

15e

0

0

0

]2,0,0[. 333131

^^

eeeP p

)(2233

133331333131

c

cee

a

aaeePP

AlGaN

AlGaNGaNp

zPE

http://www.tamu.edu/http://engineering.tamu.edu/http://www.tamu.edu/http://engineering.tamu.edu/

Degree of Relaxation

• Any strained epitaxial films

will have partial, spatially

dependant relaxation below

the critical thickness (Tc)

• Above Tc, full relaxation

occurs and the only

polarization left is PSP

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0

0.2

0.4

0.6

0.8

1

Al Mole Fraction, x

De

gre

e o

f R

ela

xa

tio

n, r(

x)

r(x) = 3.5 (x - 0.35)

)()](1[233

133331

c

cee

a

aaxrP

AlGaN

AlGaNGaNPE

GaNrelaxedAlGaN

GaNstrainedAlGaN

aa

aaxr

,

,)(

]1),(5.3min[

0)(

1xxxr

1

0

1

1

xx

xx

http://www.tamu.edu/http://engineering.tamu.edu/

Parametric numerical modeling

of polarization

• Any field above Ecrit

will result in device

failure

• Collapse to universal

polarization above Tc

)/(3.342.8, CmMVxE AlGaNcrit

http://www.tamu.edu/http://engineering.tamu.edu/

Resulting Sheet Carrier Density

• Consistently greater

than 1012 cm-3 sheet

charge density

• We now have a

parametric design

template for

concentration in terms

of Al fraction and

thickness

0 0.1 0.2 0.3 0.4 0.5 0.6 0.71012

1013

Al Mole Fraction, x

2D

EG

Sh

ee

t C

arr

ier

Co

nce

ntr

atio

n (

1/C

m2

)

d = 6nm

d = 10nm

d = 20nm

d = 30nm

d = 40nm

d = 50nm

][)(2

0CFb

AlGaNs EEe

deen

GaNSPAlGaNPEAlGaNSP PPP ,,,

)(84.03.1 eVxe b

)(7.02.1 2 eVxxEC

s

AlGaN

sF n

m

n

m

eE

*

23/2

*

0

2

]88

9[

http://www.tamu.edu/http://engineering.tamu.edu/

And (almost) finally…2DEG

resistivity

• Now we can design

our device

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7300

500

700

900

1100

1500

1900

2300

2700

3500

4300

5000

Al Mole Fraction, x

2D

EG

Sh

ee

t R

esis

tivity (

Oh

ms)

d = 6nm

d = 10nm

d = 20nm

d = 30nm

d = 40nm

d = 50nm

ss

DEGen

1

2

http://www.tamu.edu/http://engineering.tamu.edu/

Device consideration

• Our goal is to use the

2DEG sheet resistance to

create a device that

uniformly drops 5kV

without any formation of

electric field above Ecrit

gdgdx LVE /

22

xPAlGaN EEE

EAlGaN = Ecrit,AlGaN

2222222

, )/()/( gdBRPgdgdPxPAlGaNcrit LVELVEEEE

22

,/ PAlGaNcritBRgd EEVL

http://www.tamu.edu/http://engineering.tamu.edu/

Breakdown in GaN

• Peizoelectric field is

negligible in GaN

• Smaller subset of

previous Lgd

parameters due to

substrate breakdown

2

0

,22'2'2 )()(GaN

GaNSP

gd

dg

SPxGaN

P

L

VEEE

2

0

,22

, )()(GaN

GaNSP

gd

BRGaNcrit

P

L

VE

http://www.tamu.edu/http://engineering.tamu.edu/

0 0.1 0.2 0.3 0.4 0.5 0.6 0.710

-1

100

101

102

103

104

Al Mole Fraction, xD

rain

Re

sis

tan

ce

(m

illi O

hm

s.C

m2

)

d = 6nm

d = 10nm

d = 20nm

d = 30nm

d = 40nm

d = 50nm

The result

• A full set of design

parameters that allow

HV design with ultra-

low on-state resistance

– AlGaN Thickness

– AlGaN concentration

– Gate-drain distance

• Need corroboration!

http://www.tamu.edu/http://engineering.tamu.edu/

Outline

• Motivation

• GaN design for 5kV

• Additional device and integration needs

• Summary

http://www.tamu.edu/http://engineering.tamu.edu/

Caveat Emptor…

• Other consideration that we are researching

– Enhancement mode operation

– GaN breakdown to substrate

– Alternate electric field smoothing techniques

– Thermal management

http://www.tamu.edu/http://engineering.tamu.edu/

Depletion HEMT to Enhancement MOSHFET

• HEMT has Negative Threshold

Voltage!

• Application of a dielectric and

high work function metal lifts

the Fermi level, removing the

equilibrium 2DEG

GaN AlyGa1-yN

ΔPInAlN-InGaN

2DEG

GaN AlyGa1-yN Metal

Φ~5.1eV

http://www.tamu.edu/http://engineering.tamu.edu/http://www.tamu.edu/http://engineering.tamu.edu/

Alternate Field Smoothing

26 July 2011

Drain Field

Plate

Gate Gate

Dielectric

Gate Field

Plate (FP)

Passivation

Dielectric

(translucent)

Source

http://www.tamu.edu/http://engineering.tamu.edu/

Summary

• Pushing high voltage design of low Ron,sp GaN

HEMT devices opens up miniaturization,

integration and efficiency options

• A first-time complete design spec outlined for HV

GaN HEMTs

• Alternate means being developed to eliminate

additional device design constraints