  We report a new biphasic crystalline wurtzite/zinc-blende homostructure in
gallium nitride nanowires. Cathodoluminescence was used to quantitatively
measure the wurtzite and zinc-blende band gaps. High resolution transmission
electron microscopy was used to identify distinct wurtzite and zinc-blende
crystalline phases within single nanowires through the use of selected area
electron diffraction, electron dispersive spectroscopy, electron energy loss
spectroscopy, and fast Fourier transform techniques. A mechanism for growth is
identified.
