Structural and thermal effects of ion-irradiation induced defect configurations in silicon

Classical molecular dynamics calculations were used to investigate the formation of defects produced during irradiation of energetic ions on silicon. The aim of this study was to characterize the nature of defects and defective regions formed through ion irradiation and to establish a connection between the ion irradiation parameters, lattice defect configurations, and the resulting modified lattice thermal conductivity of silicon. The defective regions were characterized according to the total number of defects generated, the size and the density of the defective region, and the longitudinal and radial distribution of defects along the ion impact path. In addition, the clustering of the defects into amorphous pockets is analyzed and the effect of these processing parameters on the properties of the clusters is also studied. Further, the lattice defect configurations produced during continuous bombardment of multiple ions are directly investigated and compared to the single-ion impact results. A range of irradiation parameters including ion species, ion energies, fluence, and beam width have been explored to elucidate the dependence of the resulting defect configurations on these experimental design parameters. High density defective regions are found to be produced by low-energy ions with high atomic number. Analysis of the defects produced under varying beam diameters indicates that the beam diameter, rather than the beam energy, is the more prominent factor in determining the extent of the defective region. We demonstrate that the thermal conductivity of the material is most significantly influenced by the effective diameter of the defective region, making the beam diameter the most influential experimental parameter for tuning the lattice thermal conductivity. A reduction in thermal conductivity of up to 80% from pristine silicon was achieved with the processing parameters used in this work. This study indicates that ion beam irradiation can be a realizable manufacturing process with high tunability and control to achieve desired material properties.