Regrown Ohmic Contacts to

InxGa1-xAs Approaching the

Quantum Conductivity Limit

Jeremy J. M. Law,a,b Andy D . Carter,a Sanghoon Lee,a Arthur C. Gossard,a,b and Mark J. W. Rodwella

Device Research Conference, June 19, 2012

a) Department of Electrical and Computer Engineering, University of California, Santa Barbara

b) Materials Department, University of California, Santa Barbara

Outline

•Motivation

•Ballistic FET Current and TLM Quantum Conductance

•Process Flow

•Sample Structures

− Regrowth TLM (RGTLM)

− Transmission Line Measurement (TLM)

•Results

− Metal-semiconductor (TLM)

− Metal-semiconductor and semiconductor-channel (RGTLM)

•Theory Comparison

•Conclusion

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Motivation

• Two interfaces of interest– Metal–regrowth interface

– Regrowth–channel interface

• Sheet resistance of regrowth

• Sheet resistance of ungated region

• Must ascertain contribution to overall access resistance from all of above

Source/Drain–Channel

Metal–Source/DrainUngated Channel

Unmetalized Source/Drain

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FET Ballistic Current = TLM Quantum Conductance • Fundamental limits to contact resistance to a two-dimensional channel?• Quantum limited contact resistance1, 2 equivalent to ballistic transconductance

4 1 P. M. Solomon et al., IEDM Tech. Dig., 1989, p. 405; 2 J Guo et al., IEEE Elec. Dev. Lett. 33, 525 (2012).

Regrowth TLM (RGTLM) Process Flow

Epi growth Dummy Pillar Definition Regrowth

Planarization Isolation S/D Metalization

• Understand source (regrowth) to channel interface• Rudimentary process flow• Approximates FET structure and process flow

– Independent of high-k properties• Four-point Kelvin measurement

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TLM Process Flow

Epi growth Regrowth

Isolation S/D Metalization

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• Understand metal to source (regrowth) interface

• Rudimentary process flow

• Can be done on same die as RGTLM

• Four-point Kelvin measurement

Sample Structures: TLM

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InAs RG on d–doped 25 nm In0.53Ga0.47As channel

InAs RG on 100 nm n+ In0.53Ga0.47As channel

InAs RG on d–doped 15 nm InAs channel

In0.53Ga0.47As → InAs RG on 100 nm n+ In0.53Ga0.47As channel

TLM Results

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InAs RG on d–doped 25 nm In0.53Ga0.47As channel

InAs RG on 100 nm n+ In0.53Ga0.47As channel

InAs RG on d–doped 15 nm InAs channel

In0.53Ga0.47As → InAs RG on 100 nm n+ In0.53Ga0.47As channel

Slope: 23.8 W; Intercept/2: 2.1 W–mm

Slope: 19.3 W; Intercept/2: 3.0 W–mm Slope: 11.3 W; Intercept/2: 3.0 W–mm

Slope: 7.4 W; Intercept/2: 4.6 W–mm

Sample Structures: RGTLM

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InAs RG on d–doped 25 nm In0.53Ga0.47As channel

InAs RG on 100 nm n+ In0.53Ga0.47As channel

InAs RG on d–doped 15 nm InAs channel

In0.53Ga0.47As → InAs RG on 100 nm n+ In0.53Ga0.47As channel

Regrowth TLM Results

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InAs RG on d–doped 25 nm In0.53Ga0.47As channel

InAs RG on 100 nm n+ In0.53Ga0.47As channel

InAs RG on d–doped 15 nm InAs channel

In0.53Ga0.47As → InAs RG on 100 nm n+ In0.53Ga0.47As channel

Slope: 540 W; Intercept/2: 120.8 W–mm

Slope: 32 W; Intercept/2: 55.6 W–mm

Slope: 269 W; Intercept/2: 68.2 W–mm Slope: 15 W; Intercept/2: 12.7 W–mm

Results Summary

N+ Regrowth

Composition InAs InAs InAs In0.53Ga0.47As → InAs

Thickness 60 nm 60 nm 60 nm 60 nm

Doping 5-10×1019 cm-3 5-10×1019 cm-3 5-10×1019 cm-3 5-10×1019 cm-3

Sheet Resistivity 23.8 W 7.4 W 19.3 W 11.3 W

Channel

Composition In0.53Ga0.47As In0.53Ga0.47As InAs In0.53Ga0.47As

Thickness 25 nm 100 nm 15 nm 100 nm

Doping 9×1012 cm-2 3-5×1019 cm-3 9×1012 cm-2 3-5×1019 cm-3

Sheet Resistivity 540 W 32 W 269 W 15 W

Access Resistivity 120.8 -W mm 55.6 -W mm 68.2 -W mm 12.7 -W mmMetal/Regrowth Contact Resistivity 2.1 -W mm

0.2 -W mm24.6 -W mm1.5 -W mm2

3.0 -W mm0.4 -W mm2

3.0 -W mm0.8 -W mm2

• Contact resistance to thin channels (small ns) limited by quantum conductance

• Low contact resistance of 12.7 W–mm (11.1 W–mm2)• Contact resistance low ns channels 136.4 W–mm close to theoretical 80 W–

mm

Conclusion

• Ballistic FET current equivalent to quantum conductance of TLM

• Should not add to FET contact resistance

• Material independent, i.e. true for all semiconductor materials

• Metal–regrowth contact resistance is small portion of overall Rc

– ~ 3.0 W–mm (1.0 W–mm2)

• Regrown ohmic contacts (136 W–mm) within a factor of 2 of theoretical 80 W–mm

• 12.7 W–mm (11.1 W–mm2) is true measure of interface properties– This includes regrowth to channel and metal to regrowth

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Backup slides

MBE Regrowth by Migration Enhance Epitaxy (MEE)

InAs Quasi MEE

In, As, and Si shutters open As shutter open

InGaAs Quasi MEE

In, Ga, As, and Si shutters open As shutter open

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MBE Regrowth: Close to 2-D Quantum conductivity Limit:

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