Atomistic modeling of ion channeling in Si with point defects: the role of lattice relaxation

We report the results of the simulation of ion-channeling spectra in a disordered silicon crystal, where lattice relaxation in the neighborhood of point defects, calculated by the application of empirical potentials, is taken into account. We show that, in general, the backscattering yield increases when the perfectly symmetrical configurations of point defects in the unperturbed lattice are allowed to relax. The yield enhancement depends on the potential used, the point defect type, and the beam-lattice alignment condition. A quantitative correlation between the microscopic disorder and the macroscopic yield measured by ion channeling, has been determined under the condition of a low concentration of weakly interacting point defects. The practical consequences of introducing relaxation in the interpretation of Rutherford backscattering-channeling spectra are pointed out and discussed. One important result is that if relaxation effects are neglected (as in damage models used so far), the amount of defects extracted from channeling analysis may be appreciably overestimated. The method developed here has been applied to the study of the damage distribution in the near surface of a Si sample implanted with high energy ions. In spite of the simplified description of damage in terms of point defects, our preliminary results show that taking into account lattice relaxation in ion-channeling simulation allows simultaneous fitting of backscattering spectra collected along different axial alignment conditions. The same result cannot be achieved using the standard description based on unrelaxed defects.