MOLECULAR-DYNAMICS AND QUASIDYNAMICS SIMULATIONS OF LOW-ENERGY PARTICLE BOMBARDMENT EFFECTS DURING VAPOR-PHASE CRYSTAL-GROWTH - PRODUCTION AND ANNIHILATION OF DEFECTS DUE TO 50 EV SI INCIDENT ON (2 X 1)-TERMINATED SI(001)

Molecular dynamics and quasidynamics simulations, utilizing the Tersoff many-body potential, were used to investigate projectile incorporation and defect production as well as lattice relaxation, diffusion, and annihilation of defects resulting from 50 eV Si irradiation of (2 X 1)-terminated Si(001). A unity trapping probability, in sites distributed between the epitaxial overlayer and the fourth lattice layer (l = 4), was obtained for Si projectiles irradiating an array of high- and low-symmetry points in the primitive surface unit cell. Exchange epitaxy events were observed in which a lattice atom came to rest at an epitaxial (1 X 1) bridge site while the projectile stopped in a substitutional lattice site. In addition, several collision sequences resulted in the opening of additional dimers, up to four per irradiation event, thus providing (1 X 1 ) sites for migrating adatoms during ion-assisted crystal growth. The primary residual lattice defects produced were split and hexagonal interstitials, although tetragonal, bond-centered, and pentagonal interstitials were also produced in layers l = 2 through l = 14 with the average interstitial layer depth [1] = 2.3. Calculated interstitial migration activation energies E(m) decreased toward the surface with minimum energy paths generally involving tetragonal sites. Ion-irradiation-induced interstitials can thus be easily annealed out over time periods corresponding to the deposition of less than one monolayer under typical Si molecular-beam-epitaxy conditions. Fewer vacancies were produced, although they have a higher migration activation energy, and they were distributed over a shallower depth, 1 less-than-or-equal-to 7. Complete annealing of ion-irradiation-induced vacancies requires interaction with deeper interstitials, moving toward the surface, and incident Si projectiles.