Strain engineering in lattice-mismatched core/shell nanowires: extending the properties of GaAs


Strain engineering in lattice-mismatched core/shell nanowires: extending the properties of GaAs

Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Shan, S.; Fotev, I.; Pashkin, A.; Ghorbani-Asl, M.; Krasheninnikov, A.; Wolf, D.; Hlawacek, G.; Schneider, H.; Helm, M.; Dimakis, E.

Strain engineering in core/shell nanowires (NWs) can be an alternative route to tailor the properties of III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/InxGa1-xAs or GaAs/InxAl1-xAs core/shell NWs can sustain unusually large misfit strains that would have been impossible in equivalent thin-film heterostructures, and undergoes a significant modification of its electronic properties.
Self-catalyzed core/shell NWs were grown on SiOx/Si(111) by MBE (Fig. 1a). The growth conditions were optimized in order to minimize the bending of the NWs, a phenomenon that originates from the large misfit between the core and the shell. Synchrotron X-ray diffraction and Raman scattering measurements showed that for a given core diameter, the magnitude and the spatial distribution of the built-in misfit strain can be regulated via the composition and the thickness of the shell. Beyond a critical shell thickness (Fig. 1b), we obtain a heavily tensile-strained core and a strain-free shell. The tensile strain of the core exhibits a quasi-hydrostatic character and causes the reduction of the GaAs band gap energy in accordance with our theoretical predictions (deformation potential theory and first principle calculations), reaching the remarkable value of 40% (0.87 eV at 300 K) for 7% of strain (x = 0.54). Signatures of valence-band splitting were also identified in polarization-resolved photoluminescence measurements, as a result of the strain anisotropy in GaAs. Presuming a reduced effective mass of electrons in the tensile-strained core of GaAs/InxAl1-xAs NWs (core diameter = 22 nm, x = 0.39–0.49), the corresponding electron mobility was measured by optical-pump THz-probe spectroscopy to be in the range of 4000 cm2/V·s at 300 K. These values are the highest reported, even in comparison to GaAs/AlxGa1-xAs NWs with double the core thickness.
In conclusion, our results (unpublished) demonstrate the possibility to resemble to a large extent the fundamental properties of InxGa1-xAs alloys using strained GaAs NWs grown epitaxially on Si (Fig. 1c). This could open a new dimension in the design of nano-photonics and nano-electronics, surmounting issues with phase separation, surface segregation or alloy disorder that typically exist in ternary alloys and limit the device performance.

Keywords: optoelectronics; band gap reduction; InxGa1-xAs

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Publ.-Id: 27606