The GaN/AlN system grown on SiC(000 (1) over bar) by plasma assisted molecular-beam epitaxy presents N-polarity. Based on reflection high-energy electron diffraction (RHEED) experiments, we demonstrate that 1 ML of Ga behaves as a surfactant during the growth of GaN on AlN(000 (1) over bar) surface, which makes possible to synthesize GaN quantum dots using the Modified Stranski-Krastanow growth mode. The N-polarity GaN islands formed on AlN (000 (1) over bar) are hexagonal pyramids with {1 (1) over bar 0 (3) over bar} facets. The island density can be controlled in the 3 - 9 x 10(10) cm(-2) range.