thus paves the way for the important applications spreading from negative refraction, [1][2][3] chiral sensing [4,5] to production of optical field carrying out optical angular momentum for quantum information applications. [6] It has been shown that plasmonic nanostructures forming 1D [7] elements, 2D metasurfaces, [8][9][10] and 3D metamaterials [11] can exhibit linear chiral response due to their own, intrinsic chirality. Also semiconductor nanostructures can exhibit chiral features. [12][13][14][15][16] From the optical point of view, chiral structures possess the ability to rotate the plane of the polarization of electromagnetic waves (optical activity), and give rise to circular dichroism-i.e., the difference in the absorption of right-and lefthanded circular polarized light.Apart from 3D chiral objects, the possibility to obtain optical chirality, i.e., optical activity, with nonchiral elements was studied in the past, [17] but only recently reconsidered. [18,19] This phenomenon is obtained when the experimental configuration composed by both the nonchiral object and the optical incident field is nonsuperimposable on its mirror image. [20] This is called "extrinsic" chirality; in our previous works we have investigated this type of chirality in tilted golden nanowires by means of both linear (reflection and absorption) and nonlinear (second harmonic generation) measurements. [20][21][22][23] III-V semiconductor nanowires (NWs) have been widely investigated since they exhibit good waveguiding properties thus offering a light manipulation at nanoscale. Coupling of the incident light to the discrete leaky waveguide modes above the bandgap in NWs leads to increased resonant absorption, thus paving the way for important applications such as energy harvesting, spectral selectivity, lasing, spin angular momentum generation, etc. [24][25][26][27] Metallic NWs have also been investigated for plasmonic laser applications [28][29][30] and possibility of surface plasmon polaritons excitation. [31] One step further is the partial covering of such NWs with gold: this can induce, along with the proper experiment setup, the symmetry breaking which leads to chiral response.In this paper, for the first time to our knowledge, we report on a circular dichroism behavior from semiconductor hexagonal Semiconductor nanostructures hybridized with metals have been known to offer new opportunities in nonlinear optics, plasmonics, lasing, biosensors; among them GaAs-based nanowires (NWs) hybridized with gold can offer new functionalities, as chiral sensing and light manipulation, as well as circular polarization sources. This study investigates GaAs-AlGaAs-GaAs NWs fabricated by self-catalyzed growth on Si substrates, and partially covered with gold, thus inducing the symmetry breaking and a potential chiral response. Three different samples are investigated, each of them with a different morphology, as the length and the overall diameter ranging from 4.6 to 5.19 µm and from 138 up to 165 nm, respectively. The samples are first char...

Dopant atoms can be incorporated into nanowires either via the vapor-liquid-solid mechanism through the catalyst droplet or by the vapor-solid growth on the sidewalls. Si is a typical n-type dopant for GaAs, but in nanowires it often suffers from a strongly amphoteric nature in the vapor-liquid-solid process. This issue can be avoided by using Te, which is a promising but less common alternative for n-type doping of GaAs nanowires. Here, we present a detailed investigation of Te-doped self-catalyzed GaAs nanowires. We use several complementary experimental techniques, such as atom probe tomography, off-axis electron holography, micro-Raman spectroscopy, and single-nanowire transport characterization, to assess the Te concentration, the free-electron concentration, and the built-in potential in Te-doped GaAs nanowires. By combing the experimental results with a theoretical model, we show that Te atoms are mainly incorporated by the vapor-liquid-solid process through the Ga droplet, which leads to both axial and radial dopant gradients due to Te diffusion inside the nanowires and competition between axial elongation and radial growth of nanowires. Furthermore, by comparing the free-electron concentration from Raman spectroscopy and the Te-atom concentrations from atom probe tomography, we show that the activation of Te donor atoms is 100% at a doping level of 4 × 10 18 cm −3 , which is a significant result in terms of future device applications.

Chiral optical response is an inherent property of molecules and nanostructures, which cannot be superimposed on their mirror images. In specific cases, optical chirality can be observed also for symmetric structures. This so-called extrinsic chirality requires that the mirror symmetry is broken by the geometry of the structure together with the incident or emission angle of light. From the fabrication point of view, the benefit of extrinsic chirality is that there is no need to induce structural chirality at nanoscale. This paper reports demonstration extrinsic chirality of photoluminescence emission from asymmetrically Au-coated GaAs-AlGaAs-GaAs core-shell nanowires fabricated on silicon by a completely lithography-free self-assembled method. In particular, the extrinsic chirality of PL emission is shown to originate from a strong symmetry breaking of fundamental HE11 waveguide modes due to the presence of the asymmetric Au coating, causing preferential emission of left and right-handed emissions in different directions in the far field.