As each implanted ion enters the target, it undergoes a series of collisions with the target atoms until it finally comes to rest at some depth Rp.

There are two different mechanisms of energy loss.

1. Nuclear Stopping:

Nuclear stopping is carried by a collision between two atoms, and can be described by classical kinematics.

Nuclear stopping is elastic in nature and the energy lost by the incoming ion is transferred to the target atom, which is recoiled away from its lattice site.

This process is responsible for the production of lattice disorder and most of the damage to the crystal structure of the target material.

Nuclear stopping is due to the energy transfer from the ion to Si nuclei.

The interaction may be strong enough to displace the Si atom from its site (only 15 eV needed to displace one Si atom).

The displaced Si atom may even have enough kinetic energy to displace several other Si atoms.

Arsenic and Phosphorous ions lose their energy mostly by nuclear stopping.

Often the semiconductor becomes amorphous and/or semi-insulating.

Nuclear stopping is more important at lower atomic number (lighter elements) and lower ion velocities (low acceleration energy/voltage).

2. Electron Stopping:

Electronic stopping is caused by interaction with the electrons of the target.

Electronic stopping is inelastic in nature and the energy lost by incident ions is dissipated through the electron cloud into thermal vibrations of the target material.

In the process, the bound electrons become free electrons, because they gain the energy and that is called electronic stopping.

Electronic stopping is due to the energy transfer from the ion to the electrons of the host Si crystal. Boron ions lose their energy mostly by electronic stopping.

Electronic stopping does not cause crystal damage.

Electronic stopping dominates at higher atomic number (heavier elements) and higher ion energies.

The total stopping power S of the target, defined as the energy (E) loss per unit path length of the ion(x), is the sum of these two terms:

$S=\bigg(\frac{dE}{dx}\bigg)_{nuclear}+\bigg(\frac{dE}{dx}\bigg)_{electronic}$

The relative importance of the two processes depends on the energy E and the atomic number Z of the ion. Note that nuclear collisions dominate at low energies and electronic collisions at high energies. For light ions electronic collisions will dominate whereas for heavier ions nuclear collisions will dominate.