The damage buildup in Ge and GaAs bombarded at room and elevated temperatures by keV Ne+ and Ar+ ions has been studied. Results show that the accumulation of disorder can be considered as a planar growth of an amorphous layer proceeding from the surface. A retardation of amorphous layer growth is experimentally observed in Ge for low ion doses. Results (for the case of room temperature irradiation of GaAs and for all the cases of irradiation of Ge except for the case of irradiation by Ar+ ions with high ion flux density) are explained based on the diffusion of mobile point defects to the surface with a subsequent interface segregation process. Calculations based on this model are in good agreement with experimental data. (c) 2005 Elsevier B.V. All rights reserved.