Elastic properties of GaAs during amorphization by ion implantation

Line-focus beam acoustic microscopy has been used to study changes in the elastic constants of GaAs during amorphization produced by implantation with Si+ ions at liquid-nitrogen temperature. The distribution of amorphous material was determined by Rutherford backscattering and channeling. Values of c11 and c44 were estimated by fitting theoretical curves to the measured angular dispersion of surface acoustic waves in the (001) plane. The implanted material was modeled as a statically stressed anisotropic layer on an unmodified GaAs substrate. The values of c11 and c44 were found to decrease with increasing ion fluence. At the highest fluence the implanted region was completely amorphous, and it was observed that the softening of c44(41%) was significantly greater than that of c11(17%).