  We perform correlated studies of individual GaN nanowires in scanning
electron microscopy combined to low temperature cathodoluminescence,
microphotoluminescence, and scanning transmission electron microscopy. We show
that some nanowires exhibit well localized regions emitting light at the energy
of a stacking fault bound exciton (3.42 eV) and are able to observe the
presence of a single stacking fault in these regions. Precise measurements of
the cathodoluminescence signal in the vicinity of the stacking fault give
access to the exciton diffusion length near this location.
