Effect of collision cascade density on swelling and surface topography of GaN

We study the surface topography and swelling of GaN irradiated at room temperature with 1.3 keV/amu F, P, PF2, and PF4 ions. These irradiation conditions reveal the effect of the collision cascade density on ion-induced swelling and roughening of the GaN surface. Results show that, for F and P ions that create dilute collision cascades, swelling dominates erosion. In the case of molecular ion irradiation, characterized by larger cascade densities, surface erosion dominates swelling. For the conditions studied, surface roughness scales with the thickness of surface amorphous layers when these layers are thinner than about 20 nm.