Raman scattering of a single freestanding rolled up SiGe/Si tube R. Songmuang and O. G. Schmidt Max-Planck-Institut für Festkörperforschung Stuttgart, Germany Acknowledgment N. Y. Jin-Phillipp Max-Planck-Institut für Metallforschung Stuttgart, Germany MBE group Max-Planck-Institut für Festkörperforschung Stuttgart, Germany

2 Outline Introduction -Basic mechanism -Fabrication process Experiment -TEM and selected area electron diffraction -Raman spectroscopy -Local annealing process Conclusions

3 Introduction : 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 process Due to strain relaxation of the compressive strained layer V. Ya. Prinz et. al., Physica E 6, 828 (2000).

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

5 Introduction : Fabrication process Applications Applications - 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 materials C. 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

6 Experiment : Freestanding tubes Create freestanding tubes

7 Experiment : 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

8 Experiment : Raman spectroscopy

9 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 Si 0.67 Ge 0.33 /17 nm Si

10 Experiment : 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 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).

11 Strained Relaxed Measure Experiment : Raman spectroscopy Samples  Si-Si in SiGe layer(cm -1 )  Si-Si in Si layer(cm -1 ) 10 nm Si 0.50 Ge 0.50 /9 nm Si 493 ( 507, 489)515 ( 503, 520) 10 nm Si 0.64 Ge 0.36 /8 nm Si 498 ( 510, 498)515 ( 508, 520) 10 nm Si 0.67 Ge 0.33 /17 nm Si 502 ( 511, 500)517 ( 509, 520) 10 nm Si 0.67 Ge 0.33 /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

12 Schematic of a local annealing process Experiment : Local annealing

13 Experiment : Local annealing Si-Si vibration peak evolution during annealing process

14 Experiment : Local annealing Raman spectrum before and after annealing Annealed at 4.0 mW 40 min.

15 Experiment : Local annealing Raman spectrum before and after annealing Annealed at 4.0 mW 5 min.

16 Conclusions 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.