GaAs-based nanowires partially covered with gold give rise to optical circular dichroism

Hybridized nanostructures composed by metals and dielectrics, semiconductors or organics offer new opportunities achieving new functionalities in nonlinear optics, plasmonics, sensing [1-4]. In particular GaAs- AlGaAs-GaAs core-shell-supershell nanowires (NWs) fabricated by self-catalyzed growth on Si substrates werepartially covered with gold, thus producing a symmetry breaking in the sample geometry that induces an “extrinsic” chiral response. The possibility to obtain optical activity with non-chiral elements was studied in the past [5], but only recently reconsidered [6,7]. This phenomenon is obtained when the experimental configuration composed by both the non-chiral object and the optical incident field is non-superimposable on its mirror image [8-10]. Here we use the photo-acoustic technique with circular polarised light to put into evidence the different absorption for circular polarizations of opposite headedness when the light impinges on such structures under a proper oblique angle [11], see Fig.1. The investigated samples are formed by NWs which length is about 5 micron and 140nm in diameter. The measure circular dichroism gives the highest response at about 20° of incident light. The obtained results are encouraging and our current efforts are dedicated to the development of prototype chiral photodetectors based on such structures including pn-junctions for collecting the charge carriers