Growth of pure wurtzite InGaAs nanowires for photovoltaic and energy harvesting applications

Abstract

Vertically aligned and dense InGaAs nanowires were grown on Si (111) substrates by Au-assisted molecular beam epitaxy, and their antireflection characteristics were studied. The bandgap of InGaAs nanowires was tuned to be about 1.0 eV by adjusting the In to Ga ratio. The grown nanowires were vertically aligned with a diameter of similar to 20 nm near the top and similar to 44 nm at the bottom, with a slightly tapered structure. This tapered nanostructure was formed due to the different surface diffusivities and affinities of In and Ga to the Au catalyst. The grown InGaAs nanowires have no significant stacking, kinking, and bending defects. High-resolution transmission electron microscopy study showed that the grown InGaAs nanowires have a pure wurtzite single crystalline structure with the maximum length of similar to 18 mu m. Photo-reflectometry measurement showed a significant reduction in the reflectance less than similar to 5% at normal incidence in the wavelength range of 200-1700 nm. In addition, spectroscopic ellipsometry study showed a reduced reflectance at various incident angles of 30-70 degrees in the wavelength range of 200-1100 nm. These optical investigations demonstrate the antireflection characteristics of the InGaAs nanowires. Furthermore, piezoelectric responses were collected from the top of the vertically standing InGaAs nanowires at five different points using piezoelectric force microscopy. The measured area for one point was about 50 nm x 50 nm, and the piezoelectric responses of one or two InGaAs nanowires per point were expected to be measured, as the growth direction was along with the polar c-axis [0001] direction.