Direct simulation of ion-beam-induced stressing and amorphization of silicon

Using molecular dynamics simulation, we investigate the mechanical response of silicon to high-dose ion irradiation. We employ a realistic and efficie nt model to directly simulate ion-beam-induced amorphization. Structural pr operties of the amorphized sample are compared with experimental data and r esults of other simulation studies. We find that the behavior of the irradi ated material is related to the rate at which it can relax. Depending upon the ability to deform, we observe either the generation of a high compressi ve stress and subsequent expansion of the material or the generation of ten sile stress and densification. We note that statistical material properties , such as radial distribution functions, are not sufficient to differentiat e between different densities of amorphous samples. For any reasonable defo rmation rate, we observe an expansion of the target upon amorphization in a greement with experimental observations. This is in contrast to simulations of quenching which usually result in denser structures relative to crystal line Si. We conclude that although there is substantial agreement between e xperimental measurements and most simulation results, the amorphous structu res being investigated may have fundamental differences; the difference in density can be attributed to local defects within the amorphous network. Fi nally we show that annealing simulations of our amorphized samples can lead to a reduction of high-energy local defects without a large-scale rearrang ement of the amorphous network. This supports the proposal that defects in amorphous silicon an analogous to those in crystalline silicon. [S0163-1829 (99)08741-X].