Defect accumulation during channeled erbium implantation into GaN

Abstract

Gallium nitride films epitaxially grown on sapphire, were irradiated at room temperature with 80keVEr+166 or 170keVEr2+166 ions to fluences ranging from 1×1013cm−2 to 1×1015cm−2. 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⟨0001⟩ axis, i.e., channeled implantation, and compared to random implantation, i.e., the conventional geometry in which the ion beam is tilted 10° off the GaN c axis. For this purpose, Rutherford backscattering and channeling spectrometry and high-resolution x-ray diffraction were used. The defect concentration and the maximum perpendicular strain exhibit the same increasing trend with the ion fluence. Three regimes can 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 remains low due to an effective dynamic annealing process. In the second fluence regime, the defect concentration rises sharply, which is characteristic for nucleation-limited amorphization and finally, a third regime is 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 is found at a significantly higher erbium fluence compared to random implantation.