N(+)ions at 50 keV were implanted up to a fluence of 3 x 10 cm into a (001) GaAs substrate capped by a 125-nm Si(3)N(4)layer obtained by sputtering deposition. The Si N-3 (4)/GaAs system was kept at 450 degrees C during ion implantation. Nitrogen bubbles were present on both sides of the Si3N4/GaAs interface of the as-implanted sample, which showed a layered structure. In addition, the N-implanted region on the GaAs side was almost amorphous. By subsequent thermal annealing at 850 degrees C for 5 min under N (2)flow, we were able to synthesize a GaN nanolayer with the wurtzite structure. We also identified cubic-structured GaN with a lattice parameter of (0.42 +/- 0.01) nm, which is significantly smaller than the one reported in the literature (0.45 nm) for the GaN zinc-blend phase.