The GaN piezoelectric nanowires (NWs) are considered as promising nanomaterials to develop high-efficient piezoelectric generators.

We analyse the electrical and optical propreties of single GaN nanowire p-n junctions grown by plasma-assisted molecular-beam epitaxy using magnesium and silicon as doping sources. Different junction architectures having either a n-base or a p-base structure are compared using optical and electrical analyses. Electron-beam induced current microscopy of the nanowires shows that in the case of a n-base p-n junction the parasitic radial growth enhanced by the Mg doping leads to a mixed axial-radial behavior with strong wire-to-wire fluctuations of the junction position and shape. By reverting the doping order p-base p-n junctions with a purely axial well-defined structure and a low wire-to-wire dispersion are achieved. The good optical quality of the top n nanowire segment grown on a p-doped stem is preserved. A hole concentration in the p-doped segment exceeding 10 18 cm -3 was extracted from electron beam induced current mapping and photoluminescence analyses. This high concentration is reached without degrading the nanowire morphology.