Ultra-Wide Bandgap AlGaN Channel MISFET with Heterostructure … · Ultra-Wide Bandgap AlGaN...

DRC2016 Sanyam Bajaj: [email protected] Prof. Siddharth Rajan: [email protected]

Ultra-Wide Bandgap AlGaN Channel

MISFET with Heterostructure

Engineered Ohmics

Sanyam Bajaj1, F. Akyol1, S. Krishnamoorthy1, Y. Zhang1, S. Rajan1

1Department of Electrical and Computer Engineering

The Ohio State University, Columbus, OH USA

A. Armstrong2, A. Allerman2

2Sandia National Laboratories, Albuquerque, NM USA

Acknowledgment:

ONR (Dr. Paul Maki), NSF (ECCS-1408416), Raytheon IDS Microelectronics

mailto:[email protected]



Outline

2

• Motivation

• Heterostructure engineered ohmics

• MISFET device operation




Outline

3

• Motivation






Applications – III-Nitrides

4

III-Nitrides

High composition AlGaN with large bandgap / breakdown field:- Next-generation High Power RF amplification / Switching

- Optoelectronics / Deep-UV emitters

Dissertation, Pil Sung Park,

OSU (2013)




UWBG Material Systems

5

Properties 4H-SiC GaN Ga2O3 C AlN

Bandgap (eV) 3.3 3.4 4.9 5.5 6.2

Breakdown Field

(MV/cm)

2.5 3.3 8 10 12-16 [1]

Saturation velocity,

vsat (cm/s)

2x107 2x107 -- ~2x107 ~2.2x107 [2]

JFOM = Ecvsat /2π

(x107 MV/s)

0.8 1.1 2.5 3.2 3.8 - 5

Relative dielectric

constant (ε)

9.7 9 10 5.5 8.5

Electron mobility

(cm2/Vs)

1000 2000 300 2000 800 [3]

BFOM/BFOMSi

(εμEC3)

340 1450 3500 24660 > 26350

Polarization YES YES

UWBG AlGaN:- Extremely high (theoretical) critical breakdown field > 12 MV/cm

1Hudgins et al. IEEE Trans. on 18.3 (2003) 2Farahmand et al. IEEE Trans. on 48.3 (2001) 3Bajaj et al. APL 105.26 (2014)





6


Bandgap (eV) 3.3 3.4 4.9 5.5 6.2

Breakdown Field

(MV/cm)

2.5 3.3 8 10 12-16 [1]


vsat (cm/s)

2x107 2x107 -- ~2x107 ~2.2x107 [2]

JFOM = Ecvsat /2π

(x107 MV/s)

0.8 1.1 2.5 3.2 3.8 - 5

Relative dielectric

constant (ε)

9.7 9 10 5.5 8.5

Electron mobility

(cm2/Vs)

1000 2000 300 2000 800 [3]

BFOM/BFOMSi

(εμEC3)

340 1450 3500 24660 > 26350



- High saturation velocity predicted (Monte Carlo calculations) – more research needed to

confirm experimentally






7


Bandgap (eV) 3.3 3.4 4.9 5.5 6.2

Breakdown Field

(MV/cm)

2.5 3.3 8 10 12-16 [1]


vsat (cm/s)

2x107 2x107 -- ~2x107 ~2.2x107 [2]

JFOM = Ecvsat /2π

(x107 MV/s)

0.8 1.1 2.5 3.2 3.8 - 5

Relative dielectric

constant (ε)

9.7 9 10 5.5 8.5

Electron mobility

(cm2/Vs)

1000 2000 300 2000 800 [3]

BFOM/BFOMSi

(εμEC3)

340 1450 3500 24660 > 26350



- High saturation velocity predicted (Monte Carlo calculations) – more research needed to

confirm experimentally

- Superior Johnson’s FOM and Baliga’s FOM – ideal for high power / high temperature / high

frequency applications





Outline

8

• Motivation






Challenge: Ohmic Contact Formation

9

WBG semiconductors –

1. Low electron affinity

2. Low dopant ionization

• Result in large tunneling barrier

and width for electrons – low

tunneling probability, high RC

EF

ECΦB

EVAC

ΦM χS

Metal Semiconductor

e-

e

Wm b

eT 3

*24 2/1




Challenge: Ohmic Contact Formation

10

EF

ECΦB

EVAC

ΦM χS

e-

EF

EC

EVAC

ΦM χS

ΔEC

AlGaN channel HEMT

structure: challenging to

achieve alloyed ohmics

• Electron affinity of AlGaN lower

than GaN

• Difficulty in spiking metal through

high Al composition in barrier

layer

WBG semiconductors –

1. Low electron affinity

2. Low dopant ionization

• Result in large tunneling barrier

and width for electrons – low

tunneling probability, high RC




Previous work in Literature

11

0.3 0.4 0.5 0.6 0.7 0.81E-5

1E-4

1E-3

0.01

0.1

Yafune et al.

IEEE El.Lett.

(2014)

Yafune et al.

JJAP (2011)

Nanjo et al.

APL (2008)

Yafune et al.

JJAP (2011)

C (

.cm

2)

Al composition in AlGaN channel

Previous work on AlGaN channel HEMTs:1) Zr/Al/Mo/Au metal-based alloyed ohmic contacts up to 60% AlGaN channel [Yafune

et al., 2014]

EF

EC

EVAC

ΦM χS

ΔEC





12

0.3 0.4 0.5 0.6 0.7 0.81E-5

1E-4

1E-3

0.01

0.1

Yafune et al.

IEEE El.Lett.

(2014)

Yafune et al.

JJAP (2011)

Nanjo et al.

APL (2008)

Yafune et al.

JJAP (2011)

C (

.cm

2)



et al., 2014]

2) Ion-implantation + alloying to achieve ohmic contacts up to 38% AlGaN channel

[Nanjo et al., 2008]

EF

EC

EVAC

ΦM χS

ΔEC





13

0.3 0.4 0.5 0.6 0.7 0.81E-5

1E-4

1E-3

0.01

0.1

Yafune et al.

IEEE El.Lett.

(2014)

Yafune et al.

JJAP (2011)

Nanjo et al.

APL (2008)

Yafune et al.

JJAP (2011)

C (

.cm

2)



et al., 2014]

2) Ion-implantation + alloying to achieve ohmic contacts up to 38% AlGaN channel

[Nanjo et al., 2008]

- Contact resistance increased with higher Al composition in channel and barrier layers

EF

EC

EVAC

ΦM χS

ΔEC




Heterostructure-Engineered Ohmics

14

A A’

High composition

n-AlGaN channel

S DA

A’

EF

EC

EV

AlGaNΦB

• Conduction band profile under the contacts – n-type doped wide

bandgap AlGaN with large Schottky barrier height





15

High composition

n-AlGaN channel

Reverse graded

n++ AlGaN -> GaN

S D

A’

A

EC

A A’

• Contact layer with reverse polarization-grading to GaN

• High doping concentration to compensate negative polarization

charges (reduce sheet resistance of contact layers)

EV

GaN

n++

Polarization grading

ΦB

EF

AlGaN





16

High composition

n-AlGaN channel

Reverse graded

n++ AlGaN -> GaN

S D

A’

A

EC

A A’

• Contact layer with reverse polarization-grading to GaN

• High doping concentration to compensate negative polarization

charges (reduce sheet resistance of contact layers)

• This approach does not require regrowth (challenging for high

composition AlGaN due to surface oxidation / GaN decomposition)

EV

GaN

n++

Polarization grading

ΦB

EF

AlGaN




Experiment – n-type Al0.75Ga0.25N Channel

17

30nm Al0.75Ga0.25N (UID)

AlN on Sapphire

100nm Al0.75Ga0.25N

Si = 3x1019 cm-3

75%

6%50nm Graded

n++ AlGaN

Si = 1020 cm-3

- 100 nm 75% n-AlGaN channel with EG = 5.35 eV (MBE growth on

AlN/Sapphire template)

- Si donor concentration = 3x1019 cm-3

- 50 nm n++ reverse polarization-graded contact layer

- Conduction band profile under ohmic region (as-grown)

A’

A

A A’

0 50 100 150 200-6

-4

-2

0

2

4

6

UID

AlGaN

AlNn-Al0.75

Ga0.25

N

Graded AlGaN

EF

EV

En

erg

y (

eV

)

Distance (nm)

AS GROWN:

Contact regionE

C





AlN on Sapphire

90nm Al0.75Ga0.25N

Si = 3x1019 cm-3

75%

6%

- 100 nm 75% n-AlGaN channel with EG = 5.35 eV (MBE growth on

AlN/Sapphire template)

- Si donor concentration = 3x1019 cm-3

- 50 nm n++ reverse polarization-graded contact layer

- Conduction band profile under gate region (recessed)

A

A’

100 150 200-6

-4

-2

0

2

4

6

UID

AlGaN

En

erg

y (

eV

)

Distance (nm)

RECESSED:

Intrinsic region

n-Al0.75

Ga0.25

N AlN

EC

EF

EV

A A’

Experiment – n-type Al0.75Ga0.25N Channel




XRD and AFM

19

- X-ray diffraction scan to confirm AlGaN channel / graded contact layer

- Atomic-Force Microscopy to confirm smooth surface morphology (as-

grown surface)

rms~1.1 nm




Contact Resistance using TLM

20

Graded AlGaN

contact layer

30nm Al0.75Ga0.25N

(UID)

AlN on Sapphire

AlGaN channel

Non-alloyed ohmic contacts – Ti/Al/Ni/Au = 20/120/30/50 nm

S D





21

30nm Al0.75Ga0.25N

(UID)

AlN on Sapphire

AlGaN channel

S D

RC1RC1

RSH

spacing

0 1 2 3 4 5 6 7

4

6

8

10

12

14

SP = 1.4x10-6 .cm2

RC1

= 0.15 .mm

RSH

= 158 /sq

Resis

tance (

ohm

)

Spacing (m)

Non-alloyed ohmic contacts – Ti/Al/Ni/Au = 20/120/30/50 nm

As-grown structure:• RC1 (Metal-

semiconductor interface

resistance) = 0.15 Ω.mm

• ρSP = 1.4x10-6

Ω.cm2

Recessed structure:• Net RC to 75% AlGaN

channel = 0.32 Ω.mm

• ρSP = 1.9x10-6

Ω.cm2





22

30nm Al0.75Ga0.25N

(UID)

AlN on Sapphire

AlGaN channel

S D

RC1RC1

RSH

spacing

0 1 2 3 4 5 6 7

4

6

8

10

12

14

SP = 1.4x10-6 .cm2

RC1

= 0.15 .mm

RSH

= 158 /sq

Resis

tance (

ohm

)

Spacing (m)

As-grown structure:• RC1 (Metal-

semiconductor interface

resistance) = 0.15 Ω.mm

• ρSP = 1.4x10-6

Ω.cm2

Recessed structure:• Net RC to 75% AlGaN

channel = 0.32 Ω.mm

• ρSP = 1.9x10-6

Ω.cm2

30nm Al0.75Ga0.25N

(UID)

AlN on Sapphire

75nm channel

S D

RC1RC1

RSH1 RSH2RSH1

spacing

2 4 6 8 10 12 1420

30

40

50

60

70

80

90

100

110

SP = 1.9x10-6 .cm2

RC1

+RSH1

= 0.32 .mm

RSH2

= 725 /sq

Resis

tance (

ohm

)

Spacing (m)

Cl2-based ICP-RIE etch to test contact to AlGaN channel





23

30nm Al0.75Ga0.25N

(UID)

AlN on Sapphire

AlGaN channel

S D

RC1RC1

RSH

spacing

0 1 2 3 4 5 6 7

4

6

8

10

12

14

SP = 1.4x10-6 .cm2

RC1

= 0.15 .mm

RSH

= 158 /sq

Resis

tance (

ohm

)

Spacing (m)

• ρSP = 1.9x10-6

Ω.cm2

30nm Al0.75Ga0.25N

(UID)

AlN on Sapphire

75nm channel

S D

RC1RC1

RSH1 RSH2RSH1

spacing

2 4 6 8 10 12 1420

30

40

50

60

70

80

90

100

110

SP = 1.9x10-6 .cm2

RC1

+RSH1

= 0.32 .mm

RSH2

= 725 /sq

Resis

tance (

ohm

)

Spacing (m)

0.3 0.4 0.5 0.6 0.7 0.8

1E-6

1E-5

1E-4

1E-3

0.01

0.1

Yafune et al.

IEEE El.Lett.

(2014)

Yafune et al.

JJAP (2011)

Nanjo et al.

APL (2008)

This work

Yafune et al.

JJAP (2011)

C (

.cm

2)


Record-low ρSP to Wide bandgap AlGaN > 5 eV (Non-alloyed)




Outline

24

• Motivation






Al0.75Ga0.25N Channel MIS-FET

25


AlN on Sapphire

7nm n-AlGaN channel

S D

20nm Al2O3

G

- Recessed structure with 7 nm

n-Al0.75Ga0.25N channel

- 20 nm ALD Al2O3 followed by

700°C PDA (30s)

- C-V / doping profile confirmed

donor concentration and channel

thickness – some depletion at 0

bias

25 30 35 400

1

2

3

4

ND (

x1

019cm

-3)

Depletion (nm)

-14 -12 -10 -8 -6 -4 -2 00.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

V (Volts)

C (F

/cm

2)

100 kHz

GS S

D





26

0 2 4 6 8 100

10

20

30

40

50L

G = 1 m, L

GD = 2 m

VG = -1 V

I D (

mA

/mm

)

VDS

(V)

VG = 2 V

-6 -4 -2 0 20

2

4

6

8

10

VGS

(V)

gm (

mS

/mm

)

0

10

20

30

40

I D (

mA

/mm

)

VDS

= 10 V30nm Al0.75Ga0.25N (UID)

AlN on Sapphire

7nm n-AlGaN channel

S D

20nm Al2O3

G25 30 35 40

0

1

2

3

4

ND (

x1

019cm

-3)

Depletion (nm)

- IDS_MAX > 40 mA/mm ; gm_MAX = 10 mS/mm (limited by low channel

mobility of 15 cm2/Vs)

- High Si doping needed to overcome defect related compensation –

expect higher mobility with lower dopant concentration

-14 -12 -10 -8 -6 -4 -2 00.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

V (Volts)

C (F

/cm

2)

100 kHz

- Recessed structure with 7 nm



700°C PDA (30s)




bias





27

0 2 4 6 8 100

10

20

30

40

50L

G = 1 m, L

GD = 2 m

VG = -1 V

I D (

mA

/mm

)

VDS

(V)

VG = 2 V

-6 -4 -2 0 20

2

4

6

8

10

VGS

(V)

gm (

mS

/mm

)

0

10

20

30

40

I D (

mA

/mm

)

VDS

= 10 V30nm Al0.75Ga0.25N (UID)

AlN on Sapphire

7nm n-AlGaN channel

S D

20nm Al2O3

G25 30 35 40

0

1

2

3

4

ND (

x1

019cm

-3)

Depletion (nm)

- IDS_MAX > 40 mA/mm ; gm_MAX = 10 mS/mm (limited by low channel

mobility of 15 cm2/Vs)

- High Si doping needed to overcome defect related compensation –

expect higher mobility with lower dopant concentration

- Low 2-terminal diode breakdown due to high net charge in the channel

(~ 5x1013 cm-2)

-14 -12 -10 -8 -6 -4 -2 00.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

V (Volts)

C (F

/cm

2)

100 kHz

-14-12-10 -8 -6 -4 -2 0 21E-8

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

10

I G (

A/c

m2)

VG (V)

Diode Radius

= 100 m- Recessed structure with 7 nm



700°C PDA (30s)




bias




SUMMARY

28

- Achieved record-low specific contact resistance to UWBG

Al0.75Ga0.25N channel (NON-ALLOYED)

- Heterostructure engineered ohmics to UWBG AlGaN –

polarization-graded + doped contact layers

- Demonstrated the 1st UWBG Al0.75Ga0.25N channel MISFET

with low-resistance ohmics (MBE)

- This work removes one of the principle challenges for

UWBG AlGaN devices; applications in large range of

electronic and photonic devices

0.3 0.4 0.5 0.6 0.7 0.8

1E-6

1E-5

1E-4

1E-3

0.01

0.1

Yafune et al.

IEEE El.Lett.

(2014)

Yafune et al.

JJAP (2011)

Nanjo et al.

APL (2008)

This work

Yafune et al.

JJAP (2011)

C (

.cm

2)


30nm Al0.75Ga0.25N

(UID)

AlN on Sapphire

75nm channel

S D

RC1RC1

RSH1 RSH2RSH1

spacing

2 4 6 8 10 12 1420

30

40

50

60

70

80

90

100

110

SP = 1.9x10-6 .cm2

RC1

+RSH1

= 0.32 .mm

RSH2

= 725 /sq

Resis

tance (

ohm

)

Spacing (m)

0 2 4 6 8 100

10

20

30

40

50L

G = 1 m, L

GD = 2 m

VG = -1 V

I D (

mA

/mm

)

VDS

(V)

VG = 2 V



Ultra-Wide Bandgap AlGaN Channel MISFET with Heterostructure … · Ultra-Wide Bandgap AlGaN...

Documents

Transcript of Ultra-Wide Bandgap AlGaN Channel MISFET with Heterostructure … · Ultra-Wide Bandgap AlGaN...