InGaAs - SemaTech

ISAGST 2010, Troy, NY September 28-30, 2010

Electron Scattering in Buried InGaAs/High-k MOS Channels

S. Oktyabrsky, P. Nagaiah, T. Chidambaram V. Tokranov, M. Yakimov, and R. Kambhampati College of Nanoscale Science and Engineering, University at Albany-SUNY, Albany, NY

D. Veksler, G. Bersuker, and N. Goel, International SEMATECH, Albany, NY

College of Nanoscale Science and Engineering

Outline • InGaAs based MOSFETs with high-k dielectrics: challenges • Mobility in buried n-type QW channels: • Top semiconductor barrier • Temperature • Electron density

• Annealing • Interface control using in-situ a-Si passivation • Summary


III-V MOSFETs: Challenges InAs regrown contact

• High quality interface with dielectric

High-k oxide gate metal

• Low density of interface states • High thermal stability of the interface (challenge for implant activation)

spacer

Channel: InGaAs

SI Substrate: GaAs or InP

• Improvement of channel mobility • Low mass: Scattering – Coulomb, roughness, remote soft phonons • Buried channel – increased tox, higher power • Spacer – 5 nm (tox  +1.7nm)

~8000-15000 cm2/V-s in GaAs or InGaAs

spacer ~1500-2000

cm2/V-s

• S-D resistance • Regrown InAs for n-type or InSb on p-type

in GaAs or InGaAs

• p-channel mobility/drain current (goal: CMOS) m*

From Weber et al. SSE 2006

• Strain • III-Sb • Ge


n-MOSFET with Buried In0.53Ga0.47As/InP Channel and in situ HfO2 Reactive e-beam deposition

Effective channel mobility 10000

2k

InP

/sq

/sq

.

.

/sq

Uncorrected Charge-corrected .

Hall mobility at Vg=0V

2

InP

Mobility, cm /V-s

5k

1k

Drain and gate leakage current HfO2 on In0.52Al0.48As L/W= 80 m /80 m

HfO2 on 2ML In0.53Ga0.47As

1000

L/W=10 m/370 m 100

10

12

13

10

Sheet carrier concentration, cm

-2

• Effective channel mobility 1300cm2/V-s • Hall mobility of 1800 cm2/V-s at 3x1012 cm-2 • Significant reduction of Dit 2ML in HfO2 /2ML InGaAs • SS from 2.2 V/dec  150 mV/dec

J. Cryst. Growth 2008


n-InGaAs Buried QWs: Experimental Goal:

Space of Variables: • QW • In content 77%

- baseline for QW MOSFET mobility (Hall measurements) - main scattering mechanisms Motivation: -Very little data on mobility in QW channels -Unreliable data on MOSFETs -Another method to characterize interface Variations of doping (50 nm thick barrier)

• Thickness 10 nm • Top Barrier • Thickness

High-k

• Oxide • HfO2 reactive e-beam deposition • ALD ZrO2, Al2O3, Al2O3+ZrO2 • No interface passivation or a-Si IPL • Modulation Doping

InAlAs

5 nm spacer, -doping

In0.77GaAs QW 5 nm spacer, -doping n = 1.8x1012 cm-2 2 5 nm spacer = 7990 cm /V-s = 435 /sq. bulk-doping

InAlAs

• Bulk below QW

• Processing • RTA 400-600 0C

n = 1.3x1012 cm-2 = 14300 cm2/V-s = 328 /sq.

InP:Fe

n = 1.5x1012 cm-2 = 11400 cm2/V-s = 375 /sq.


n-InGaAs Buried QWs: Transport vs. Semiconductor Barrier Thickness InAlAs/InGaAs

RT transport in 10 nm In0.77Ga0.23As QWs 11400

10000

2

In0.77GaAs QW 5 nm spacer Mod.-doping InAlAs

PVD- HfO2 ALD- ZrO2 ALD- Al2O3 ALD- Al2O3+ ZrO2

Hall Mobility, cm /V-s

High-k

InP:Fe

• n ~ (1-3)x1012 cm-2 (in high-mobility samples) • Clear dependence of mobility on db • ~1.5x higher mobility with ALD oxides • Remote scattering due to interface and oxide

5000

PVD HfO2 ALD Al2O3+ZrO2 ALD ZrO2 ALD Al2O3

2000

1000 0

1

2

3

4

5

6

7

50

Semicond. Barrier thickness, nm College of Nanoscale Science and Engineering

Scattering Mechanisms Zhu and Ma, EDL, 25, 89 (2004)

• Bulk III-V: • Phonon scattering • Ionized impurities scattering • etc. + • Remote charge scattering (RCS): • Is caused by interfacial states and bulk oxide charges, >0: RCS

bT

• Remote phonon scattering (RPS): • Caused by phonons in high-k oxide • Should have different trend vs. T, >0 Ph HK

Laikhtman and Solomon, JAP, 103, 014501 (2008)

CT

• Interface roughness: • Exponentially decrease with the barrier thickness SR

const


n-InGaAs Buried QWs: Temperature dependence of mobility 10 nm InGaAs/InAlAs QWs (from Matsuoka, JJAP 1990)

Mobility in QWs vs. T and d (HfO2)

~T

2


100000

-1.2

dB = 50nm

10000

7nm 5nm 3nm 1nm 0nm

1000

~T 100

1.0 200

300

Si/HfO2 and Si/SiO2 (from Maitra, JAP 2007)

Temperature, K

• Deep QWs – phonon-limited mobility, •

~T-1.2

~T-1.2

vs. T dependence reverses at d=5 nm (at

~ 4000 at RT)

• Approaching ~T+1.0 at small d - likely remote Coulomb scattering (RCS) • Si channels - do not show positive slope, though slope reduces with high-k’s College of Nanoscale Science and Engineering

Theoretical (low-mobility samples) • Poisson equation with Stern-Howard screening • 2D scattering, Fermi statistics

Calculations of RCS mobility are performed following (Barraud et al Microel. Eng. 2007, 84, 2404; JAP 2008, 104, 073725)

• Isotropic effective mass • Kubo-Greenwood formulation for mobility

Solid -experiment; open - theory

• Single fitting parameter: Number of

Thick barrier - Phonon scattering dominates with (T) ~T-1.2 Thin barriers - Coulomb scattering

~T

2

• Nt = 2x1013 cm-2 at the highk/barrier interface assumed in calculations

100000


trapped charges at the high-k/barrier interface

-1.2

50nm

10000

7nm 5nm 3nm 1nm

1000

~T 100

150

1.0 200

250 300 350 400

Temperature, K


Issues with the explanation 1) Need to identify the nature of 2x1013 cm-2 charges

2) At room temperature there is significant deviation between theory and experiment T at 300K Int

Acceptors

Dit

EF

CNL Donors Donors are neutral if filed Acceptors are neutral if empty The Fermi level is close to the CNL – number of charged traps is small College of Nanoscale Science and Engineering

Low-mobility samples: Transport activation • Activation type dependence of conductivity vs. temperature is observed

Conductivity, (Ohm/sq.)

-1

0.8meV

• Activation energy decreases with higher carrier density

• Activation energy is lower at higher conductivity

1E-3

• Conductivity saturates at low temperature (as for typical localization)

10meV 6meV

Instead of scattering at the Remote charges potential one may consider percolation in this potential:

3.5meV

13.5 1E-4

10meV 40meV 34meV

0.000

0.005

0.010

1/T (K)

0.015 -1

From: http://terpconnect.umd.edu/~enrossi/research.html


Activation energy

EF +/- 3kT

Potential in the channel

Activation energy at RT, meV

Low mobility and it’s dependence vs. temperature can be explained by hoping

10

1

1E12

Electron Density, cm

•

With ns increase Ef becomes higher

•

With T increase more energetic electrons exist

1E13 -2


High-mobility samples: T-dependence Experimental and interface-related Mobility vs. T=10-300K

Electron mobility of ALD Gate Stacks with 3nm semiconductor barrier 1.E+05

Bulk QW ZrO2

Mobility, cm2/VS

5nm

1.E+04 ALD ZrO2, 3nm

1.E+03 10

100

T, K

• Similar trends as with PVD HFO2:

• Phonon-like in high mobility samples • Flattens and RCS-like in low-mobility samples • Crossover is at ~3000 cm2/Vs • Mobility saturates at T20,000


Summary 

Baseline QW mobility vs. top semiconductor barrier thickness and electron density is evaluated



Mobility does not directly affected by Dit but mainly determined by remote fixed charges/dipols at the High-K/III-V interface, in both “low mobility” and “high mobility” samples



vs. T differs for ZrO2 and Al2O3+ZrO2 samples – likely competition of RCS and remote phonons scattering



Low mobility values in some samples at low carrier density and their temperature dependences may be explained by hopping and associated with hopping carrier activation



a-Si IPL is valuable for InGaAs/InP system if high-T annealing is used

Funding: • SEMATECH • INTEL Corporation • FCRP/DARPA (MSD) College of Nanoscale Science and Engineering