High Yield of GaAs Nanowire Arrays on Si Mediated by the Pinning and Contact Angle of Ga.

GaAs nanowire arrays on silicon offer great perspectives in the optoelectronics and solar cell industry. To fulfill this potential, gold-free growth in predetermined positions should be achieved. Ga-assisted growth of GaAs nanowires in the form of array has been shown to be challenging and difficult to reproduce. In this work, we provide some of the key elements for obtaining a high yield of GaAs nanowires on patterned Si in a reproducible way: contact angle and pinning of the Ga droplet inside the apertures achieved by the modification of the surface properties of the nanoscale areas exposed to growth. As an example, an amorphous silicon layer between the crystalline substrate and the oxide mask results in a contact angle around 90°, leading to a high yield of vertical nanowires. Another example for tuning the contact angle is anticipated, native oxide with controlled thickness. This work opens new perspectives for the rational and reproducible growth of GaAs nanowire arrays on silicon.

Enhanced second harmonic generation from InAs nano-wing structures on silicon.

We demonstrate morphology-dependent second-harmonic generation (SHG) from InAs V-shaped nanomembranes. We show SHG correlation with the nano-wing shape and size, experimentally quantify the SHG efficiency, and demonstrate a maximum SHG enhancement of about 500 compared to the bulk. Experimental data are supported by rigorous calculations of local electromagnetic field spectra.

Vertical "III-V" V-shaped nanomembranes epitaxially grown on a patterned Si[001] substrate and their enhanced light scattering.

We report on a new form of III-V compound semiconductor nanostructures growing epitaxially as vertical V-shaped nanomembranes on Si(001) and study their light-scattering properties. Precise position control of the InAs nanostructures in regular arrays is demonstrated by bottom-up synthesis using molecular beam epitaxy in nanoscale apertures on a SiO(2) mask. The InAs V-shaped nanomembranes are found to originate from the two opposite facets of a rectangular pyramidal island nucleus and extend along two opposite <111> B directions, forming flat {110} walls. Dark-field scattering experiments, in combination with light-scattering theory, show the presence of distinctive shape-dependent optical resonances significantly enhancing the local intensity of incident electromagnetic fields over tunable spectral regions. These new nanostructures could have interesting potential in nanosensors, infrared light emitters, and nonlinear optical elements.