The GaP-ZnO core-shell nanowire (NW) heterojunction integrated on top of a multi-junction solar cell can extend its spectral sensitivity region toward shorter wavelengths, enhance the photon absorption, and reduce the surface light reflection. We report on the preparation of the Zn-doped GaP cores for such heterostructure NWs. Problems with NW Zn doping are addressed. A small amount of diethylzinc (DEZn) vapor added to the reactor slightly increased the axial and radial growth rates, which resulted in moderate increase in NW tapering. A further increase in the DEZn molar fraction in the reactor suppressed the tapering (lower radial growth rate) but the axial growth rate was increased. When the DEZn molar fraction exceeded 9 x 10(-6), the NW growth was hindered; only small stumps and kinked wires grew. The measurement of NW electrical transport parameters showed that DEZn compensated native n-type impurities at small vapor pressures (chi(DEZn) similar to 1 x 10(-8) to 1 x 10(-7)); the NWs exhibited n-type conductivity or were compensated. GaP NWs of p-type with a hole concentration p similar to 1 x 10(18) cm(-3) were grown only in a very narrow interval of DEZn vapor pressures (chi(DEZn) similar to 1-6 x 10(-6)). (C) 2012 Elsevier B. V. All rights reserved.