Gallium nitride films, epitaxially grown on sapphire, were irradiated at room temperature with 80keV 166Er+ or 170keV 166Er2+ ions to fluences ranging from 1013 to 1015/cm2. The defects induced by ion implantation (as a result of the nuclear energy transfer) generate a perpendicular elastic strain in the hexagonal GaN lattice. The accumulation of lattice damage and lattice deformation were investigated for Er ions impinging along the GaN<00▪1> axis, i.e., channelled implantation, and compared to random implantation, i.e., the conventional geometry in which the ion beam was tilted 10° off the GaN c axis. For this purpose, Rutherford backscattering and channelling spectrometry and high-resolution X-ray diffraction were used. The defect concentration and the maximum perpendicular strain exhibited the same increasing trend with the ion fluence. Three regimes could be distinguished for both implantation geometries, for low fluences (corresponding to a value below 1 displacement per atom in case of random implantation), the defect concentration remained low due to an effective dynamic annealing process. In the second fluence regime, the defect concentration rises sharply, which was characteristic for nucleation-limited amorphization and finally, a third regime was found where layer-by-layer amorphization of the implanted area starts from the surface. The onset of the steep increase in the case of implantations along the GaN c axis was found at a significantly higher erbium fluence compared to random implantation.

Defect Accumulation during Channeled Erbium Implantation into GaN. B.Pipeleers, S.M.Hogg, A.Vantomme: Journal of Applied Physics, 2005, 98[12], 123504 (6pp)