GaN NWs with two different doping profiles were grown on Si(111) substrates in nitrogen rich conditions without any catalyst using an AlN buffer layer. In one case Si was supplied during the first 2 hours of the growth followed by 30 min without supply of any doping species, subsequently growth was continuing for an additional 2 hours with supplying Mg (Type-A). In the other case the reverse structure was fabricated, starting with Mg doping and ending with Si doping (Type-B). For all samples of type-B, the DAP signal in PL, {mu}-PL and CL is less intense than the NBE peak and in some cases almost not detectable. In contrast Type-A samples show a very strong DAP signal. By combining PL, {mu}-PL and CL results, we concluded that during the first stages of the growth of GaN NWs, the incorporation of Mg is hampered, while in the later phase of the growth, the Mg is more effectively incorporated and acts as an acceptor in the GaN matrix.