Journal
ACS NANO
Volume 14, Issue 6, Pages 6845-6856Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsnano.0c00762
Keywords
Raman spectroscopy; nanowires; hexagonal (lonsdaleite) SiGe; resonant Raman; phonons; crystal structure transfer
Categories
Funding
- European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program [756365]
- Swiss National Science Foundation Ambizione grant [PZ00P2_179801]
- Ministerio de Economia', Industria y Competitividad (MINECO) [FEDER-MAT2017-90024-P]
- Severo Ochoa Centres of Excellence Program [SEV-2015-0496]
- Generalitat de Catalunya [2017 SGR 1506]
- European Union's Horizon 2020 research and innovation program [735008]
- Solliance, a solar energy RD initiative of ECN
- TNO
- Holst
- TU/e
- IMEC
- Forschungszentrum Julich
- Dutch province of Noord-Brabant
- Swiss National Science Foundation (SNF) [PZ00P2_179801] Funding Source: Swiss National Science Foundation (SNF)
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Recent advances in nanowire synthesis have enabled the realization of crystal phases that in bulk are attainable only under extreme conditions, i.e., high temperature and/or high pressure. For group IV semiconductors this means access to hexagonal-phase SixGe1-x nanostructures (with a 2H type of symmetry), which are predicted to have a direct band gap for x up to 0.5-0.6 and would allow the realization of easily processable optoelectronic devices. Exploiting the quasi-perfect lattice matching between GaAs and Ge, we synthesized hexagonal-phase GaAs-Ge and GaAs-SixGe1-x core-shell nanowires with x up to 0.59. By combining position-, polarization-, and excitation wavelength-dependent mu-Raman spectroscopy studies with first-principles calculations, we explore the full lattice dynamics of these materials. In particular, by obtaining frequency-composition calibration curves for the phonon modes, investigating the dependence of the phononic modes on the position along the nanowire, and exploiting resonant Raman conditions to unveil the coupling between lattice vibrations and electronic transitions, we lay the grounds for a deep understanding of the phononic properties of 2H-SixGe1-x nanostructured alloys and of their relationship with crystal quality, chemical composition, and electronic band structure.
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