The build-up of damage towards amorphization was studied, using Rutherford backscattering channelling spectrometry and transmission electron microscopy, in wurtzite-type films under keV-bombardment with 12C or 197Au ions at room temperature or liquid-N temperatures. A marked similarity was observed between the damage build-ups for light- and heavy-ion bombardment. The results suggested that there was a substantial dynamic annealing of irradiation defects; even during heavy-ion bombardment at liquid-N temperatures. The amorphization began from the surface, with increasing ion dose, for both liquid-N and room-temperature bombardment with light or heavy ions. A strong surface defect peak arose from an amorphous layer at the surface; as indicated by transmission electron microscopy. The origin of such an amorphous layer was attributed to the trapping of mobile point defects by the surface; as suggested by the flux behavior. In the case of samples which were implanted with light ions to 1015/cm2, no amorphous layer at the surface was revealed by transmission electron microscopy. The damage build-up was highly sigmoidal for liquid-N temperature bombardment with light or heavy ions. The formation of planar defects in the bulk was assumed to provide nucleation sites, for amorphization, with increasing ion dose during bombardment at liquid-N temperatures. In the case of room-temperature bombardment with heavy ions, damage in the bulk saturated at a level which was lower than that of the amorphous phase and amorphization proceeded from the surface with increasing ion dose. For such a saturation regime at room temperature, the implantation damage in the bulk consisted of point-defect clusters and planar defects which were parallel to the basal plane of the film.

Damage Build-up in GaN under Ion Bombardment. S.O.Kucheyev, J.S.Williams, C.Jagadish, J.Zou, G.Li: Physical Review B, 2000, 62[11], 7510-22