Defect-induced amorphization of crystalline silicon as a mechanism of disordered-region formation during ion implantation

An atomic-scale simulation study is presented which demonstrates that siliconamorphization during ion implantation can be caused by defect-induced collapseof the crystalline lattice. The amorphization threshold is calculated in termsof critical defect concentrations required to induce the amorphizationtransition at room temperature. These concentrations are found to be about28%, 20%, and 25% of self-interstitials, vacancies, or Frenkel pairs,respectively. These high defect densities are consistent with experimentalmeasurements in silicon self-implanted with high-energy ions. The structureof the defect-induced amorphous phases is similar to that of the bulkamorphous phase produced by rapid quenching of liquid silicon.