In-plane growth of germanium nanowires on nanostructured Si(001)/SiO2 substrates

Germanium (Ge) nanowires (NWs) were grown in-plane on nano-structured Si(001)/SiO2 substrates by molecular beam epitaxy using gold (Au) as solvent. The site-selective NW growth was enabled by a rectangular array of gold droplets on silicon (Si) tips with a Au nuclei density below 0.25 µm-2 on the surrounding silicon oxide (SiO2). The initial growth of Ge NWs starting from Si-Au droplets with SixGe1-x nucleation from ternary alloy is discussed from a thermodynamic point of view. The in-plane NW elongation occurred within 〈110〉 directions on the substrate and NWs were mainly bounded by two 55° inclined {111} facets and a less pronounced planar (001) top facet. Fully relaxed crystal lattices of Ge NWs were observed from two-dimensional reciprocal space maps of X-ray diffraction measurements.