Helium irradiation effects on structural properties of A1N thin films

Structural distortion of polycrystalline A1N thin films irradiated with He and Ar ions was investigated by means of glancing angle X-ray diffraction experiments. Samples were implanted with He ions with energies from 40 to 220 keV to make a homogeneous implantantion profile and were also bombarded with 800 keV Ar ions to produce the same extent of the radiation damage due to direct atomic displacements. No phase transformation was observed throughout the whole implantation process. On the scale of the deposited energy into nuclear collisions approximately the same increase of the lattice parameter along the c-axis was observed in He- and Ar-implanted samples. On the other hand, the lattice expansion along the a-axis showed 60% larger values at the maximum fluence in the He-implanted samples than the Ar-implanted samples. The compressive strain along the a-axis also showed the larger increase in the He-implanted samples. These results suggest a preferential configuration in clustering of He atoms in the A1N crystalline lattice.