Zinc-doped gallium phosphide nanowires for photovoltaic structures

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 × 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 (χDEZn ∼ 1 × 10−8 to 1 × 10−7); the NWs exhibited n-type conductivity or were compensated. GaP NWs of p-type with a hole concentration p ∼ 1 × 1018 cm−3 were grown only in a very narrow interval of DEZn vapor pressures (χDEZn ∼ 1–6 × 10−6).