Comparison of Ultra-Thin InAs and InGaAs Quantum Wells and

Ultra-Thin-Body Surface-Channel MOSFETs

Cheng-Ying Huang1, Sanghoon Lee1, Evan Wilson3, Pengyu Long3, Michael Povolotskyi3, Varistha Chobpattana2, Susanne Stemmer2,

Arthur Gossard1,2, Gerhard Klimeck3, and Mark Rodwell1

1ECE, University of California, Santa Barbara2Materials Department, University of California, Santa Barbara

3Network for Computational Nanotechnology, Purdue University, West Lafayette, IN

CSW/IPRM 2015Santa Barbara, CA

Why III-V FETs? Why Ultra-thin channel? • III-V channel: low electron effective mass high velocity, high mobility

higher current at lower VDD reducing switching power• Channel thickness (Tch) must be scaled in proportional to gate length (Lg)

to maintain electrostatic integrity.• For ultra-thin body (UTB) MOSFETs Tch~1/4 Lg, and for FinFETs Tch~1/2 Lg. • At 7 or 5 nm nodes, channel thickness should be around 2-4 nm.• Goal: Carefully examine InGaAs and InAs channels. The best design??

WFIN~8nm

Intel 14nm FinFETMakr Bohr, IDF2014

tSi~5nm

STM-Leti-IBM 14nm UTBSOI IEDM2014

300K Si InAs InGaAs

me* 0.19 0.023 0.041

μe(cm2/V·s) 1450 33000 12000

μh(cm2/V·s) 370 450 <300

Eg(eV) 1.12 0.354 0.75

εr 11.7 15.2 13.9

a(Å) 5.43 6.0583 (InP)

Quantum confinement effects!!2

Ultra-thin channel 2DEG: Hall results

0 1 2 3 4 5 6 7 80

2000

4000

6000

8000

10000

Mobili

ty (c

m2 /V

s)

Well Thickness (nm)

InAs channel InGaAs channel

0 1 2 3 4 5 6 7 81.2

1.4

1.6

1.8

2.0

2.2

Car

rier

conce

ntr

atio

n(1

012cm

-2)

Well Thickness (nm)

InAs channel InGaAs channel

• Quantum well (QW) 2DEGs were grown by solid source MBE.

• For wide wells: μInAs > μInGaAs • For narrow wells (~2 nm):

μInAs ≈ μInGaAs • Carrier concentration decreases

due to increased E0.

3

What happens in thin wells?

0 5 10 15 200.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

InAs

In-p

lane

effec

tive

mas

s, m

// (m

0)

Well Thickness (nm)

InGaAs/InP, Nag1993 InAs/InP, Nag1993 InGaAs/InP, Wetzel1992 InGaAs/InP, Hrivnak1992 InAs, Mugny2015 Schneider1995 Wiesner1994 Wetzel1996

InGaAs

• Mobility is limited by interface roughness scattering. Strained InAs growth (S-K mode) might induce higher interface roughness.

• Electron effective mass are similar for ~2-3 nm InAs and InGaAs wells because of non-parabolic band effects.

5 10 15 20102

103

104

105

106

107

Mobili

ty (c

m2V

-1s-1

)

Well thickness(nm)

300K

total

interface roughness

remote impurity

InGaAs well

polar optical phononalloy

acoustic phonon

C. Y. Huang et al., J. Appl. Phys. 115, 123711 (2013)

µ ~Tch-6

4

J. Appl. Phys. 77, 2828 (1995), Phys. Rev. B, 52, 1038 (1996),Appl. Phys. Lett 64, 2520 (1994), Appl. Phys. Lett 62, 2416 (1993),G. Mugny et al., EUROSOI-ULSI conference 2015.

Ultra-thin body III-V FETs: Lg~40 nm

5

-0.2 0.0 0.2 0.4 0.610-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

I D (m

A/

m)

VGS

(V)

VDS

= 0.1 to 0.7 V

0.2 V increment

-0.2 0.0 0.2 0.4 0.6

g

m (mS

/m)

VGS

(V)

0.0

0.4

0.8

1.2

1.6

2.0

2.4V

DS = 0.1 to 0.7 V

0.2 V increment

0.0 0.2 0.4 0.60.0

0.5

1.0

1.5

I D (m

A/

m)

VDS

(V)

Ron

= 292 Ohm-m

at VGS

= 1.0 V

VGS

= -0.2 V to 1.0 V

0.2 V increment

0.2 0.4 0.6

VDS

(V)

Ron

= 400 Ohm-m

at VGS

= 1.0 V

VGS

= -0.2 V to 1.0 V

0.2 V increment• UTB FETs with 3 nm channels were fabricated to compare InAs and InGaAs channels.

• 1.6:1 Ion and transcoaductance for InAs channels.

• 10:1 lower Ioff for InGaAs channels.

InAs InGaAs

InGaAsInAs

On-state performance

0.1 10.0

0.4

0.8

1.2

1.6

2.0

2.4

VDS

= 0.5 V

Gate length (m)

3 nm InAs 3 nm InGaAs

Peak g

m (m

S/

m)

100 10000

100

200

300

400

5003 nm InAs3 nm InGaAs

I on (A

/m

)

Gate length (nm)

VDS

= 0.5 V

Ioff

= 100 nA/m

0.0 0.1 0.20

250

500

750

1000

RS/D

~ 19020 Ohmm

VGS

= 1 V

Ron(O

hmm

)

Gate length (m)

3 nm InAs 3 nm InGaAs

• Higher Ion and higher gm for UTB InAs FETs than InGaAs UTB FETs.

• InAs FETs achieve gm=2 mS/μm, and Ion=400 μA/μm at VDS=0.5V and Ioff=100 nA/μm.

• Similar source/drain resistance (RS/D ) ensures that the performance degradation of InGaAs is not from source/drain, but from channel itself (slope). 6

Subthreshold swing and off-state current

0.1 160

80

100

120

Gate Length (m)

Subth

reshold

Sw

ing (m

V/d

ec)

VDS

=0.1 V,3 nm InAs

VDS

=0.5 V,3 nm InAs

VDS

=0.1 V,3 nm InGaAs

VDS

=0.5 V,3 nm InGaAs

0.1 10

50

100

150

Vth at 1 A/m

DIB

L (m

V/V

)

Gate length (m)

3 nm InAs 3 nm InGaAs

100 100010-3

10-2

10-1

100

101

102

3 nm InAs3 nm InGaAs

I OFF, M

IN (nA

/m

)

Gate length (nm)

VDS

= 0.5 V

• Superior SS~83 mV/dec. and DIBL~110 mV/V because of ultra-thin channels and improved electrostatics.

• Minimum Ioff is 10:1 lower for InGaAs channel at short Lg, where leakage current limited by band-to-band tunneling.

• InGaAs FETs are limited by gate leakage at long Lg.7

Why QW-2DEGs and UTB-FETs show different results?

• 1st possible cause: Electron population in L valley due to strong quantum confinement Unlikely.

2nm InAlAs barrier, 3nm InGaAs channel with H passivation on top

Courtesy of Evan Wilson, Pengyu Long, Michael Povolotskyi, and Gerhard Klimeck.

2nm InAlAs barrier, 3nm InAs channel with H passivation on top

In0.53Ga0.47As InAs

me* at Γ [m0] 0.080 0.063

Γ – L separation [eV] 0.596 0.905

Eg at Γ [eV] 1.06 0.639 8

Why QW-2DEGs and UTB-FETs show different results?

• 2nd possible cause: Electron interaction with oxide traps inside conduction band Likely.

• Electrons in high In% content channels have less scattering and less electron capture by the oxide traps.

9

J. Robertson et al., J. Appl. Phys. 117, 112806 (2015)J. Robertson, Appl. Phys. Lett. 94, 152104 (2009)

N. Taoka et al., Trans. Electron Devices. 13, 456 (2011)N. Taoka et al., IEEE IEDM 2011, 610.

UCSB Lg~12 nm III-V MOSFETs (DRC 2015)

N+InGaAs

InP spacer

InAlAsBarrier

Lg~12nm

~ 8nm

10

tch~ 2.5 nm(1.5/1 nm InGaAs/InAs)

NiN+InP

Ion/Ioff>8.3·105

-0.2 0.0 0.2 0.4 0.6 0.810-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

gm (m

S/m

)I D (m

A/

m)

VGS

(V)

0.0

0.4

0.8

1.2

1.6

2.0

2.4

SS~107 mV/dec.SS~98 mV/dec.

VDS

= 0.1 to 0.7 V, 0.2 V increment

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70.0

0.5

1.0

1.5

I D (m

A/

m)

VDS

(V)

Ron

= 302 Ohm-m

at VGS

= 1.0 V

VGS

= -0.2 V to 1.2 V

0.2 V increment

Summary

11

• Below 10 nm logic nodes, ultrathin channels are required. • In QW 2DEGs, the electron Hall mobility are similar for

InGaAs and InAs wells as the wells thinned to 2~3nm.• In UTB MOSFETs, 3 nm InAs channels significantly improve

on-state current and transconductance (~1.6:1), and reduce channel resistance as compared to 3 nm InGaAs channel.

• Purdue’s tight-binding calculations show large ~0.6 eV Γ–L splitting in 3 nm InGaAs channels, ruling out the possibility of electron population in L-valley.

• UCSB C-V measurements show large dispersion in 3 nm InGaAs channels, possibly indicating the significant electron interactions with oxide traps. (As-As anti-bonding may be the culprit)

cyhuang@ece.ucsb.edu

Thanks for your attention!Questions?

• This research was supported by the SRC Non-classical CMOS Research Center (Task 1437.009) and GLOBALFOUNDRIES(Task 2540.001).

• A portion of this work was done in the UCSB nanofabrication facility, part of NSF funded NNIN network.

• This work was partially supported by the MRSEC Program of the National Science Foundation under Award No. DMR 1121053.

Acknowledgment

(backup slides follow)

Mobility in different channel design: 25 µm-Lg

0 1 2 3 4 5 6 70

200

400

600

800

1000

1200

Mobility

(cm

2 /Vs

)Carrier density (cm-2)

4.5 nm InGaAs 2.5 nm InAs 5.0 nm InAs

-0.2 0.0 0.2 0.4 0.6 0.80.0

0.5

1.0

1.5

2.0

2.5

3.0

Carrier d

ensity (10

12 cm-2)

Effec

tive

CG (F

/cm

2 )

VGS

(V)

0

2

4

6

8

Freq.: 200 kHzW/L=25m/21m

4.5 nm InGaAs 2.5 nm InAs 5.0 nm InAs

m*, Cg-ch, RS/D more important for ballistic FETs