Unprecedented severe atomic redistribution in germanium induced by MeV self-irradiation

We present a pronounced unprecedented surface modification of a crystalline Ge layer under ion irradiation with a Ge ion beam at the energy of 2.5 MeV. Samples were covered by a thin SiN-protection layer to protect from sputtering and surface redeposition phenomena. Under the irradiation conditions, the Ge layer did not become porous as observed for other projectiles and lower energies but develops into a severely uneven morphology with characteristic length scales of several hundred nanometers. The observed roughness monotonically increases with the irradiation doses. We show that this phenomenon is caused neither by the surface erosion effect nor by a non-uniform volumetric expansion. Rather, atomic redistribution in the bulk of the material is the major drive for the uneven surface. Furthermore, the deformation of the Ge layer likely occurs to the largest extent after irradiation, as indicated by the very flat interface around the end-of-range region. The observed morphology modification is discussed based on irradiation-induced plastic flow, coupled with a larger contribution of the electronic component in the ion–solid interactions.