Modulation doped AlGaAs/GaAs core-shell nanowire structures were grown by molecular beam epitaxy. A Si delta-doping was introduced in the AlGaAs shell around the {110} facets of the GaAs core. The wires are typically highly resistive at low temperatures. However, they show a pronounced persistent photoconductivity effect indicating activation of free carriers from the delta-doped shell to the GaAs core. The n-type character of the channel is demonstrated by applying a back-gate voltage. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim