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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.