Raman scattering of Raman scattering of a single freestanding rolled up SiGe/Si tubea single freestanding rolled up SiGe/Si tube

R. SongmuangR. Songmuang and O. G. Schmidt and O. G. SchmidtMax-Planck-Institut für FestkörperforschungMax-Planck-Institut für Festkörperforschung

Stuttgart, GermanyStuttgart, Germany

AcknowledgmentAcknowledgment

N. Y. Jin-Phillipp

Max-Planck-Institut für Metallforschung

Stuttgart, Germany

MBE group

Max-Planck-Institut für Festkörperforschung

Stuttgart, Germany

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OutlineOutline

• Introduction -Basic mechanism-Fabrication process

• Experiment-TEM and selected area electron diffraction-Raman spectroscopy-Local annealing process

• Conclusions

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Introduction : Basic mechanismIntroduction : Basic mechanism

Pseudomorphic bilayer

grown on sacrificial layer

by MBE : III-V or SiGe

material system

Release the bilayer from

the substrate

by removing sacrificial layer

Roll-up processRoll-up process

Due to strain relaxation of

the compressive strained layer

V. Ya. Prinz et. al. , Physica E 6, 828 (2000).

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Introduction : Fabrication processIntroduction : Fabrication process

S. V. Golod et. al., Semicond. Sci. Technol. 16, 181 (2001)S. V. Golod et. al., Appl. Phys. Lett. 87, 3391 (2004).

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Introduction : Introduction : Fabrication processFabrication process

ApplicationsApplications

- Micromirror created by strain-driven folding of the released semiconductor layer.

Z. Ocampo et. al. Appl. Phys. Lett. 83, 3647(2003)

- 2D channel fluid transport C. Deneke and O. G. Schmidt, Appl. Phys. Lett. 85,

2914 (2004)

- Nanoreactor to create hybrid materialsC. Deneke et. al., Appl. Phys. Lett. 84, 4475 (2004)

3D structures obtained by photolithography and RIE process

Information about wall structure and thermal stability of SiGe/Si rolled up tubes is required.

Micro-Raman spectroscopy /TEM

RIE process from G. S. Kar

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Experiment : Freestanding tubesExperiment : Freestanding tubes

Create freestanding tubes

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Experiment : Freestanding tubesExperiment : Freestanding tubes

TEM and Selected area electron diffraction (SAED)

• The splitted reflection spots are attributed to a misalignment of the bilayer.

• A non-crystalline signal is not significantly present, implying a good crystal quality of the tube wall.

TEM characterizations from N. Y. Jin-Phillipp

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Experiment : Raman spectroscopyExperiment : Raman spectroscopy

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Experiment : Raman spectroscopyExperiment : Raman spectroscopy

Raman spectra

Tube wall shows the vibration mode of

Si and SiGe layers.

Si layer : Si-Si ~516 cm-1

SiGe layer : Si-Si ~505 cm-1

Si-Ge ~400 cm-1

Ge-Ge ~290 cm-1

Raman spectra from 10 nm Si0.67Ge0.33/17 nm Si

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Experiment : Raman spectroscopyExperiment : Raman spectroscopy

Si-Si vibration mode (Si-Si)

x is Ge concentration where is the lattice mismatch between SiGe layer and substrate

J.C. Tsang et. al. J. Appl. Phys. 75, 8098 (1994).

• Ge concentration in SiGe layer

• Strain in SiGe and Si layer

35.815622.520 xsisi

• Temperature - induces a shift of the vibration mode - can be estimated by the shift of vibration mode or the Stoke and Anti- Stoke ratio - Heating effect can be avoided by using low excitation power (less than 0.4 mW)

J. S. Lannin, Phys. Rev. B 16, 1510 (1977).

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StrainedStrained Relaxed RelaxedMeasureMeasure

Experiment : Raman spectroscopyExperiment : Raman spectroscopy

Samples Si-Si in SiGe layer(cm-1) Si-Si in Si layer(cm-1)

10 nm Si0.50Ge0.50

/9 nm Si 493 ( 507, 489) 515 ( 503, 520)

10 nm Si0.64Ge0.36

/8 nm Si 498 ( 510, 498) 515 ( 508, 520)

10 nm Si0.67Ge0.33

/17 nm Si 502 ( 511, 500) 517 ( 509, 520)

10 nm Si0.67Ge0.33

/26 nm Si 504 ( 511, 500) 517 ( 509, 520)

Comparison of the measured Si-Si vibration peak with the predicted value of the strained and relaxed SiGe and Si

Assume biaxial compressive strained SiGe on Si substrate and biaxial tensile strained Si on SiGe substrate.calculated calculated

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Schematic of a local annealing process

Experiment : Local annealingExperiment : Local annealing

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Experiment : Local annealingExperiment : Local annealing

Si-Si vibration peak evolution during annealing process

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Experiment : Local annealingExperiment : Local annealing

Raman spectrum before and after annealing

Annealed at

4.0 mW 40 min.

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Experiment : Local annealingExperiment : Local annealing

Raman spectrum before and after annealing

Annealed at

4.0 mW 5 min.

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ConclusionsConclusions

• The tube wall mainly consists of crystalline SiGe/Si which shows the vibration mode corresponding to relaxed Si and SiGe layers.

• An ex-situ local laser annealing induces an irreversible change of the Ge composition of the tube wall.

• Our experiments can be viewed as a controlled method to manipulate and tune the local composition of rolled-up SiGe/Si micro- and nanotubes.