The lateral density of ZnO nanowire arrays grown with pulsed laser deposition (PLD) can be tuned from 1 to 10−2 μm−2 by introducing a ZnO nucleation layer and optimizing the distance between the substrate and the ablated target. High-density (∼10 μm−2) nanowire arrays can be grown on sapphire substrates with or without gold catalysts. However, if a ZnO wetting layer was adopted, the density of ZnO nanowires could be controlled with high reproducibility. The decreasing growth density is attributed to a competition between the two-dimensional film epitaxy and one-dimensional nanowire growth. The dependence of nanowire density on the substrate–target distance mainly arises from the expansion dynamics of the plasma plume and the chamber geometry. Using low-density nanowires as templates, a general PLD route was developed to grow radial nanowire heterostructures. Here we demonstrate MgZnO/ZnO/MgZnO nanowire quantum wells and ZnO/ZnO:P core–shell nanowire p–n junctions.
