We report the growth of dilute nitride GaNAs and GaInNAs core-multishell nanowires by plasma-assisted molecular beam epitaxy. Using constituent Ga-induced vapor-liquid-solid growth, these nanowires were grown on Si(111) and silicon on insulator (SOI) substrates. The GaNAs shell nominally contains 0%, 2%, and 3% nitrogen. We also report the growth of GaAs/GaInNAs/GaAs core-multishell nanowires nominally containing 30% In and 2% N. Axial cross-sectional scanning transmission electron microscopy measurements and energydispersive X-ray spectrometry confirm the formation of the core-multishell nanowire structure. We obtained high-quality GaNAs nanowires with nitrogen compositions up to 2%. On the other hand, GaNAs containing 3% nitrogen, and GaInNAs nanowires, show distorted structure; moreover, the optical emissions seem to be related to defects. Further optimisations of the growth conditions will improve these properties, promising future applications in nanoscale optoelectronics.
We report the crystal structures of GaAs and GaAs/GaNAs/GaAs core–multishell nanowires (NWs). From statistical investigations by x-ray diffraction (XRD) and electron backscattered diffraction (EBSD) pattern analysis, we statistically and microscopically resolve the zinc-blende (ZB) and wurtzite (WZ) polytypism within the NWs. The XRD analysis shows a smaller fraction of WZ segments in the NWs with a larger concentration of nitrogen. With increasing nitrogen content in the GaNAs shell, the ZB peak position shifts toward higher angles and the WZ peak intensity decreases. The EBSD measurements also confirm the coexistence of ZB and WZ polytypes in all of the NWs. Their polytype switches along the length. Twin defects are observed in the ZB segments in all of the NWs. The unique grain map and grain size distribution show a decrease of the WZ segments in the GaAs/GaNAs/GaAs NW, in agreement with the XRD results. Microscopically, the local area where the polytype switches from WZ in the inner-core side to ZB toward the outer-shell surface is observed. Overall, we propose that the WZ polytype in the GaAs NWs decreases because of the strain induced by the growth of the GaNAs shell with a smaller lattice constant.
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