Surface morphology of GaN bombarded by highly charged 126Xeq+ ions

N-type GaN films bombarded with different highly charged Xe-126(q+)-ions(9 <= q <= 30) at room temperature was studied by atomic force microscopy. The experimental results show that when q exceeds the threshold value 18, remarkable swelling turns into obvious erosion in the irradiated area. On the other hand, surface disorder of GaN films strongly depends on the charge state q of ions, incident angle and ion influence, and the damage behavior of films is unrelated to the kinetic energy within the scope of experimental parameters (180 keV <= E-k <= 600 keV). For q = 18, the surface morphology of the films almost does hot change at normal incidence, and at incidence angle of 30 degrees relative to the film surface, there appears small-scale swelling in irradiated region and a low step forms between the irradiated and un-irradiated regions. For q < 18, the film surface is capped with an amorphous layer, with increased roughness, distinct swelling. Moreover, especially at and near the boundaries, a series of remarkable sharp bumps like ridges are observed. And an evident step-up is formed between the irradiated and un-irradiated regions. The step is more remarkable for tilted incidence than normal incidence. For q > 18, film surface is etched, forming a deep dump with a high step with the increase of ions influence. Unambiguous indentations relevant to the ion influence on the step appear. Furthermore, the step height is proportional to the ion influence approximately and is much higher for tilted incidence than normal incidence.