Growth of branched single crystalline GaAs whiskers on Si nanowire trunks

Lugstein, Alois; Andrews, Aaron; Mathias, Steinmayr; Hyun, Yo; Bertagnolli, Emmerich; Weil, Matthias; Pongratz, Peter; Schramboeck, Matthias; Roch, Thomas; Strasser, Gottfried Austria

We present the hetero-epitaxial growth of single crystalline GaAs whiskers on Si(111)-nanowire trunks forming hierarchical star-like structures with a 6-fold symmetry. These hierarchical nanostructures have been successfully formed utilizing both, vapor-liquid-solid (VLS) growth by low pressure chemical vapor deposition (LPCVD) and molecular-beam epitaxy (MBE) techniques. High-resolution transmission electron microscopy (HRTEM) studies reveal the [111] growth direction of the core Si nanowires (Si-NWs) with six {112} facet planes. The sequentially grown branches are single crystalline GaAs nanowhiskers which grow preferably in the [111] direction and are perpendicular to the {112} facets of the Si-NW backbone. The hetero-epitaxial growth, the orientation relationship between the major Si core NW and the GaAs nanowhiskers and the good crystallinity of the Si-NWs and GaAs whiskers were confirmed by x-ray diffraction, Photoluminescence measurements, and HRTEM. PL measurements confirm a blueshift of about 30 meV compared to bulk GaAs, which can be attributed to the quantum confinement perpendicular to the growth direction. The ability to prepare rotationally branched NW structures addresses both, the long-time challenge of integrating high performance III-V semiconductors with mainstream Si technology and the possibility of monolithic 3-dimensional nanoelectronic and -photonic devices.

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