[en] With a band gap value of 1.7 eV, Al_0.2Ga_0.8As is one of the ideal III–V alloys for the development of nanowire-based Tandem Solar Cells on silicon. Nevertheless, growing self-catalysed AlGaAs nanowires on silicon by solid-source molecular beam epitaxy is a very difficult task due to the oxidation of Al adatoms by the SiO₂ layer present on the surface. Here we propose a nanowire structure including a p.i.n radial junction inside an Al_0.2Ga_0.8As shell grown on a p-GaAs core. The crystalline structure of such self-catalysed nanowires grown on an epi-ready Si(111) substrate (with a thin native SiO₂ layer) was investigated by transmission electronic microscopy and photoluminescence. I(V) measurements performed on single nanowires have shown a diode-like behaviour corresponding to the radial p.i.n junction inside the Al_0.2Ga_0.8As shell. Moreover, a current generation under the electron beam was evidenced over the entire radial junction along the nanowires by means of electron beam induced current (EBIC) microscopy. The same structure was reproduced on patterned substrates with a SiO₂ mask, producing an ordered hexagonal array. High and uniform yields from 83% to 87% of vertical nanowires were obtained on 0.9 × 0.9 cm² patterned areas. EBIC mapping performed on these nanowires confirmed the good electrical properties of the radial junction within the nanowires. (paper)