DAMAGE SATURATION DURING HIGH-ENERGY ION-IMPLANTATION OF SI1-XGEX

Saturation of radiation damage during MeV Si+-ion implantation of unstrained Si1-xGex (x=0.15,0.50) alloy layers, as well as bulk Ge, was investigated. First observed in self-ion irradiated Si, damage saturation is distinguished by a low concentration of lattice defects in the near-surface region ahead of the ions' end-of-range which remains constant over an extended range of implantation dose. A previously proposed model accounted for saturation by assuming that damage nucleates homogeneously during ion irradiation. Different mechanisms for nucleation of damage are discussed and substrate conditions are specified under which each dominates. A characteristic temperature is defined for each substrate above which damage nucleates primarily by a homogeneous mechanism. Results are presented which show the damage saturation occurs above this characteristic temperature but not below, thus establishing homogeneous nucleation as a necessary condition for the occurrence of damage saturation, as previously suggested.