III-nitride nanowires (NWs) were grown on Si(111) without catalyst by plasma-assisted molecular-beam epitaxy under N-rich conditions. The influence of doping on the morphology and electrical properties was investigated. The morphology as well as the density of GaN NWs changes with Si amount. For high Si fluxes, the wire density is reduced, in addition, the NWs broaden from bottom to top. By doping with Mg, the NW shape does not significantly change although the wires tend to coalesce. The photoelectric transport in GaN NWs is extremely sensitive to the NW diameter. This effect is used to determine the doping level. The free carrier concentration and mobility were also estimated using Raman measurements. For Si-doped InN NWs, a reduced NW density is observed, in comparison to the undoped counterpart. At high Si doping, the InN NW morphology is improved leading to more uniform diameter NWs. InN …