High crystal quality GaN nanowires doped by Mg were obtained using plasma assisted molecular beam epitaxy growth in N-rich conditions. The influence of the growth temperature on the morphology, structural and optical properties of NW growth is studied. An additional Mg flux increases the tendency of the wires to coalesce. The morphology of the doped wires with respect to their undoped counterpart is otherwise not changed. With decreasing substrate temperature the NW density decreases, at the same time the coalescence is enhanced. The samples have been investigated by means of photoluminescence (PL) as well as Raman spectroscopy. By increasing the Mg doping and reducing the deposition temperature, the ultra violet (UV) luminescence band due to Mg doping increases with respect to the near band edge emission. In addition the dominance of D{sup 0}X{sub A} emission of the near band edge peak is diminished and an increased contribution of the A{sup 0}X{sub A} can be observed. Raman spectroscopy indicates that there is no significant degradation in material quality due to Mg supply during growth.