Strain Effects on Bulk Ge Valence Band eel6935: Computational Nanoelectronics

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Strain Effects on Bulk <001> Ge Valence Band

EEL6935: Computational Nanoelectronics
Fall 2006
Andrew Koehler

Outline

Motivation
Background

Strain
Germanium

Simulation Results and Discussion
Summary
References

Motivation

Moore’s Law

~ 0.7X linear scale factor
2X increase in density / 2 years
Higher performance (~30% / 2 years)

Approaching Fundamental Limits

“No Exponential is Forever”

What is the solution?

Solution: Novel Materials

History of Strain

1954: Piezoresistance in silicon was first discovered by C. S. Smith
(resistance change due to applied stress)
1980s: Thin Si layers grown on relaxed silicon–germanium (SiGe) substrates
1990s: High-stress capping layers deposited on MOSFETs were investigated as a technique to introduce stress into the channel
1990s: SiGe incorporated in the source and drain areas
2002: Intel uses strained Si in P4 processor

What is Strain?

Stress: Limit of Force/Area as Area approaches zero
Strain: Fractional change in length of an object Distortion of a structure caused by stress

What is Strain?

Strain Effect on Valence Band

History of Germanium

1959: First germanium hybrid integrated
circuit demonstrated.
- Jack Kilby, Robert Noyce
1960: High purity silicon began replacing
germanium in transistors, diodes,
and rectifiers
2000s: Germanium transistors are still used in some stompboxes by musicians who wish to reproduce the distinctive tonal character of the "fuzz"-tone from the early rock and roll era.
2000s: Germanium is being discussed as a possible replacement of silicon???

Why Did Si Replace Ge?

Germanium’s limited availability
High Cost
Impossible to grow a stable oxide that could

Passivate the surface
Be used as an etch mask
Act as a high-quality gate insulator

Novel Materials to the Rescue

High-k Dielectric

Used as gate oxide
eliminate the issue that germanium’s native oxide is not suitable for nanoelectronics

Atomic Layer Deposition (ALD)

HfO2
ZrO2
SrTiO3, SrZrO3 and SrHfO3
ALD WN/LaAlO3/AlN gate stack

Ge vs Other Semiconductors

Future of Ge in Nanoelectronics

Researchers Believe

Combination of a Ge pMOS with a GaAs nMOS could be a manufacturable way to further increase the CMOS performance.

Current Problems

Passivation of interface states
Reduction of diode leakage
Availability of high-quality germanium-on-insulator substrates

k ∙ p method

k ∙ p method was introduced by Bardeen and Seitz
Kane’s model takes into account spin-orbit interaction

Ψnk(r) = eik∙runk(r)
unk(r+R) = unk(r) – Bloch function

n refers to band
k refers to wave vector

Useful technique for analyzing band structure near a particular point k0

k ∙ p method

Schrodinger equation
Written in terms of unk(r)

Unstressed Band Structures

Biaxial Compression 1 GPa

Longitudinal Compression 1 GPa

Band Splitting

Silicon Mass Change

Germanium Mass Change

Summary

Strain
Germanium
Strained Germanium Compared to Silicon

Unstressed
Band Splitting

Biaxial Compression
Longitudinal Compression

Mass Change - Longitudinal Compression

In-Plane
Out-of-Plane

References

C. S. Smith, “Piezoresistance effect in germanium and silicon,” Phys. Rev., vol. 94, no. 1, pp. 42–49, Apr. 1954.
R. People, J. C. Bean, D. V. Lang, A. M. Sergent, H. L. Stormer, K. W. Wecht, R. T. Lynch, and K. Baldwin, “Modulation doping in GexSi1−x/Si strained layer heterostructures,” Appl. Phys. Lett., vol. 45, no. 11, pp. 1231–1233, Dec. 1984.
S. Gannavaram, N. Pesovic, and C. Ozturk, “Low temperature (800 ◦C) recessed junction selective silicon-germanium source/drain technology for sub-70 nm CMOS,” in IEDM Tech. Dig., 2000, pp. 437–440.
S. E. Thompson and et al., "A Logic Nanotechnology Featuring Strained-Silicon," IEEE Electron Device Lett., vol. 25, pp. 191-193, 2004.
S. E. Thompson and et al., "A 90 nm Logic Technology: Part I - Featuring Strained Silicon," IEEE Trans. Electron Devices, 2004.
W. A. Brantley, "Calculated Elastic Constants for Stress Problem Associated with Semiconductor Devices," J. Appl. Phys., vol. 44, pp. 534-535, 1973.
Semiconductor on NSM, URL http://www.ioffe.rssi.ru/SVA/NSM/Semicond/.
O. Madelung, ed., Data in Science and Technology: Semiconductors-Group IV elements and III-V Compounds (Springer, Berlin, 1991).

THANK YOU

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Strain Effects on Bulk Ge Valence Band eel6935: Computational Nanoelectronics

Strain Effects on Bulk <001> Ge Valence Band

EEL6935: Computational Nanoelectronics

Fall 2006

Andrew Koehler

Outline

Motivation

Background

Simulation Results and Discussion

Summary

References

Motivation

Moore’s Law

Approaching Fundamental Limits

What is the solution?

Solution: Novel Materials

History of Strain

1954: Piezoresistance in silicon was first discovered by C. S. Smith

(resistance change due to applied stress)

1980s: Thin Si layers grown on relaxed silicon–germanium (SiGe) substrates

1990s: High-stress capping layers deposited on MOSFETs were investigated as a technique to introduce stress into the channel

1990s: SiGe incorporated in the source and drain areas

2002: Intel uses strained Si in P4 processor

What is Strain?

Stress: Limit of Force/Area as Area approaches zero

Strain: Fractional change in length of an object Distortion of a structure caused by stress

What is Strain?

Strain Effect on Valence Band

History of Germanium

1959: First germanium hybrid integrated

circuit demonstrated.

- Jack Kilby, Robert Noyce

1960: High purity silicon began replacing

germanium in transistors, diodes,

and rectifiers

2000s: Germanium transistors are still used in some stompboxes by musicians who wish to reproduce the distinctive tonal character of the "fuzz"-tone from the early rock and roll era.

2000s: Germanium is being discussed as a possible replacement of silicon???

Why Did Si Replace Ge?

Germanium’s limited availability

High Cost

Impossible to grow a stable oxide that could

Novel Materials to the Rescue

High-k Dielectric

Atomic Layer Deposition (ALD)

Ge vs Other Semiconductors

Future of Ge in Nanoelectronics

Researchers Believe

Current Problems

k ∙ p method

k ∙ p method was introduced by Bardeen and Seitz

Kane’s model takes into account spin-orbit interaction

Useful technique for analyzing band structure near a particular point k0

k ∙ p method

Schrodinger equation

Written in terms of unk(r)

Unstressed Band Structures

Biaxial Compression 1 GPa

Longitudinal Compression 1 GPa

Band Splitting

Silicon Mass Change

Germanium Mass Change

Summary

References

C. S. Smith, “Piezoresistance effect in germanium and silicon,” Phys. Rev., vol. 94, no. 1, pp. 42–49, Apr. 1954.

R. People, J. C. Bean, D. V. Lang, A. M. Sergent, H. L. Stormer, K. W. Wecht, R. T. Lynch, and K. Baldwin, “Modulation doping in GexSi1−x/Si strained layer heterostructures,” Appl. Phys. Lett., vol. 45, no. 11, pp. 1231–1233, Dec. 1984.

S. Gannavaram, N. Pesovic, and C. Ozturk, “Low temperature (800 ◦C) recessed junction selective silicon-germanium source/drain technology for sub-70 nm CMOS,” in IEDM Tech. Dig., 2000, pp. 437–440.

S. E. Thompson and et al., "A Logic Nanotechnology Featuring Strained-Silicon," IEEE Electron Device Lett., vol. 25, pp. 191-193, 2004.

S. E. Thompson and et al., "A 90 nm Logic Technology: Part I - Featuring Strained Silicon," IEEE Trans. Electron Devices, 2004.

W. A. Brantley, "Calculated Elastic Constants for Stress Problem Associated with Semiconductor Devices," J. Appl. Phys., vol. 44, pp. 534-535, 1973.

Semiconductor on NSM, URL http://www.ioffe.rssi.ru/SVA/NSM/Semicond/.

O. Madelung, ed., Data in Science and Technology: Semiconductors-Group IV elements and III-V Compounds (Springer, Berlin, 1991).

THANK YOU

**C. S. Smith, “Piezoresistance effect in germanium and silicon,” Phys. Rev., vol. 94, no. 1, pp. 42–49, Apr. 1954.**

**S. E. Thompson and et al., "A Logic Nanotechnology Featuring Strained-Silicon," IEEE Electron Device Lett., vol. 25, pp. 191-193, 2004.**

**S. E. Thompson and et al., "A 90 nm Logic Technology: Part I - Featuring Strained Silicon," IEEE Trans. Electron Devices, 2004.**

**W. A. Brantley, "Calculated Elastic Constants for Stress Problem Associated with Semiconductor Devices," J. Appl. Phys., vol. 44, pp. 534-535, 1973.**

**O. Madelung, ed., Data in Science and Technology: Semiconductors-Group IV elements and III-V Compounds (Springer, Berlin, 1991).**