  Quantum dots inserted in semiconducting nanowires are a promising platform
for the fabrication of single photon devices. However, it is difficult to fully
comprehend the electro-optical behaviour of such quantum objects without
correlated studies of the structural and optical properties on the same
nanowire. In this work, we study the spectral tunability of the emission of a
single quantum dot in a GaN nanowire by applying external bias. The nanowires
are dispersed and contacted on electron beam transparent Si3N4 membranes, so
that transmission electron microscopy observations, photocurrent and
micro-photoluminescence measurements under bias can be performed on the same
specimen. The emission from a single dot blue or red shifts when the external
electric field compensates or enhances the internal electric field generated by
the spontaneous and piezoelectric polarization. A detailed study of two
nanowire specimens emitting at 327.5 nm and 307.5 nm shows spectral shifts at
rates of 20 and 12 meV/V, respectively. Theoretical calculations facilitated by
the modelling of the
