Investigation of heavily damaged ion implanted Si by atomistic simulation of Rutherford backscattering channeling spectra

Rutherford backscattering channeling (RBS-C) spectra of ion-implanted Si are simulated according to an atomistic model of radiation damage which consists of a distribution of point defects (split-(110) interstitials and vacancies) structurally relaxed by empirical potentials. This model, successfully used to reproduce multiaxial spectra of lightly damaged Si, is applied here to the case of a heavily damaged sample. As a consequence of the increasing strain generated by lattice relaxation, simulations predict a superlinear trend of RBS-C disorder versus defect concentration in the range of intermediate damage density. This contrasts with the linear trend obtained by the usual description of defects as atoms randomly displaced in a rigid lattice. The new approach represents an improvement in the physical description of ion irradiation disorder within RBS-C analysis; however simulation results are found to be in less satisfactory agreement with spectra of a heavily damaged sample than with spectra of lightly damaged material. The description of damage as the result of the accumulation of simple point defects and the use of a static relaxation procedure instead of finite temperature molecular dynamics, are two possible reasons to explain the present limitations in describing the structural properties of heavily damaged, yet not completely amorphized, ion implanted Si.