  The Mott transition from a dipolar excitonic liquid to an electron-hole
plasma is demonstrated in a wide GaN/(Al,Ga)N quantum well at $T=7$K by means
of spatially-resolved magneto-photoluminescence spectroscopy. Increasing
optical excitation density we drive the system from the excitonic state,
characterized by a diamagnetic behavior and thus a quadratic energy dependence
on the magnetic field, to the unbound electron-hole state, characterized by a
linear shift of the emission energy with the magnetic field. The complexity of
the system requires to take into account both the density-dependence of the
exciton binding energy and the exciton-exciton interaction and correlation
energy that are of the same order of magnitude. We estimate the carrier density
at Mott transition as $n_\mathrm{Mott}\approx 2\times 10^{11}$cm$^{-2}$ and
address the role played by excitonic correlations in this process. Our results
strongly rely on the spatial resolution of the photoluminescence and the
assessment of the carrier transport. We show, that in contrast to
GaAs/(Al,Ga)As systems, where transport of dipolar magnetoexcitons is strongly
quenched by the magnetic field due to exciton mass enhancement, in GaN/(Al,Ga)N
the band parameters are such that the transport is preserved up to $9$T.
