Abstract

Semiconductor nanowires, which are characterized by high crystallinity, polarization anisotropy, and high optical nonlinearity, show great promise as nanoscale building blocks for nanophotonic devices [1]. The development of new noninvasive techniques for scrutinizing individual nanowires, preferably in their native growth environment, is therefore highly desirable. Although the growth occurs in the vertical direction, most work up to date has studied nanowires that have been detached and lie on a substrate. They can then be excited by conventional optical fields with detection of scattered signals along the substrate normal. The use of second-harmonic generation (SHG) has been shown to be very valuable for studying semiconductor assemblies due to its inherent sensitivity to structural symmetry. In order to use SHG to study vertically aligned nanowires, it is essential to tailor the excitation field so that the nanowire is illuminated with polarization along its long axis. This can be done by exciting the nanostructures at normal incidence using the longitudinal field that arises from focused radial polarization [2,3]. Here, we demonstrate that vertically aligned semiconductor nanowires, as grown on top of a semiconductor substrate, can be characterized by SHG with such focused vector beams [4].

© 2015 IEEE