Quantitative evaluation of germanium displacement induced by arsenic implantation using germanium isotope superlattices

The displacement of germanium (Ge) atoms induced by arsenic (As) ion implantation at room temperature was investigated using Ge isotope superlattices grown by molecular beam epitaxy. The depth profiles of ⁷⁴Ge isotopes in the ⁷⁰Ge/^natGe isotope superlattices before and after ion implantation were obtained by secondary ion mass spectrometry. By representing the experimental data using a conventional integral model, Ge atomic displacement as a function of depth was obtained, from which we determined that 0.75 nm is the critical displacement necessary to make the structure appear amorphous under examination by cross-sectional transmission electron microscopy. However, we found that the amorphous Ge layers were recrystallized due to a local elevation of temperature caused by the implantation, which indicates that the samples should be cooled down during implantation to avoid the regrowth of amorphous Ge layers for this analysis.