Production of amorphous zones in GaAs by the direct impact of energetic heavy ions

Abstract

The damage produced in GaAs by implantation with low energy heavy ions has been studied as a function of ion mass and implantation temperature (30 and 300 K). The experiments were performed in situ in the microscope-accelerator facility at Argonne National Laboratory. In samples implanted and examined at 30 K, spatially isolated amorphous regions were produced by the direct impact of 50 keV Ar, Kr, and Xe ions. The probability that the impact of an individual ion formed an amorphous zone increased as the ion mass increased from Ar to Kr but not from Kr to Xe. The average dimension of the amorphous zones also increased with ion mass, being greater for the Xe than for the Kr ion implantation. On warming to room temperature, the amorphous zones decreased in size and density as the sample temperature was increased above 200 K. In samples implanted and examined at 300 K, the probability of forming an amorphous zone by direct impact increased as the ion mass increased from Kr to Xe, although the probability was always less than at 30 K. The density of amorphous zones produced at 300 K was similar to that remaining in a sample implanted at 30 K and then warmed to room temperature. With time at 300 K the amorphous zones decreased in size and eventually crystallized completely, leaving no trace of their prior existence.