Damage formation and annealing studies of low energy ion implants ...

defect pairs due to Coulomb attraction and/or minimisation of local strain. For long
range migration of As the AV pair partially dissociates and the vacancy diffuses to at
least a third nearest – neighbour site in the lattice before returning along a different path.
The dopant diffusion via the interstitialcy mechanism only occurs if the AI pair does not
dissociate. The third reaction is the “kick – out” mechanism, and the fourth reaction is
the dissociative or Frank – Turnbull mechanism. They describe the behaviour of
elements that are mainly dissolved on substitutional sites but move as interstitial defects
(9, 67). These mechanisms are shown in Figure 3.13 below.
Figure 3.12 Schematic two-dimensional representations of direct
diffusion mechanisms of an element A in a solid, via a) interstitial
lattice sites and b) substitutional lattice sites. From (67).
Figure 3.13 Schematic two-dimensional representation of indirect diffusion mechanisms
of an element A in a solid. Ai, As, V, and I denote interstitially and substitutionally
dissolved foreign atoms, vacancies, and silicon self-interstitials, respectively. AV and AI
are defect pairs of the corresponding defects. From (67).
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