The morphology of the as-implanted damage in silicon is investigated using a
recently developed combination of time-ordered computer simulations based on
the binary collision approximation (BCA) with classical molecular dynamics
(MD) calculations. The method is applied to determine the type and the
amount of defects formed within the first nanosecond after ion impact. The
depth profile and the total number of different defect species (vacancies,
interstitials, disordered atoms, etc.) produced on average per incident ion
are calculated for B+ (15 keV), P+ (5, 10, 20, 30
keV), and As+ (15 keV) implantations. It is shown that the as-
implanted defect structure depends not only on the nuclear energy deposition
per ion but also explicitly on the ion mass. Therefore for each ion species
the damage morphology exhibits characteristic features. For heavy ions the
percentage of extended defects is higher than for light ions. In all cases
investigated the number of free or isolated interstitials exceeds the amount
of free vacancies. The results obtained allow a microscopic interpretation
of the phenomenological model for the as-implanted damage employed in
conventional BCA simulations in order to describe the dose dependence of the
shape of ion range profiles. They can be also applied to get more realistic
initial conditions for the simulation of the defect kinetics during
post-implantation annealing.