Group III–V compound semiconductor nanowires with radial modulation of the materials composition and/or doping in the form of core–shell and core–multishell nanowire heterostructures show promise as novel and high-performance nano-scale light emitting diodes, lasers, photodetectors and solar cells. Strict control over the growth of such radially heterostructured nanowires is, however, necessary. We report the experimental dependence of AlGaAs shell growth by metalorganic vapor phase epitaxy (MOVPE) around free-standing Au-catalysed GaAs nanowires on the relevant sizes and densities of the nanostructures. A model based on (i) the vapor mass transport of group III species, and (ii) perfect conformality between the nanowires and the substrate of AlGaAs deposition is proposed and validated, describing the observed MOVPE growth dynamics of the shell material around dense ensembles of GaAs …