A magnesium liquid metal ion source was investigated for p-type doping of GaN. The metal is an alloy composed of 33.3% Mg and 66.7% Ga. The source type is a direct heating needle source with a spring-type reservoir, which is constructed using tungsten wire and a ceramic tube. The source has been tested and characterized in a NanoFab 150 focused ion beam (FIB) system. A typical source lifetime was 250 muA h. Mg+ ion implantation of GaN thin films has been performed at different energies between 30 and 100 keV for doses ranging from 5 X 10(13) to 1 X 10(15) cm(-2). After Mg+ FIB implantation, samples were annealed at 1100degreesC in N-2 ambient. Low temperature photoluminescence with a He-Cd laser of 325 nm exhibited the donor-acceptor recombination peak, which was enhanced by the activated magnesium ions.