Stability of I3 complexes in III-V compound semiconductors by tight-binding molecular dynamics

Intrinsic interstitials in GaAs are known to have a large formation energy that makes their concentration almost negligible in as-grown materials. However, interstitials must be explicitly considered in implanted GaAs where collision cascades, induced by the energetic ions, produce a large amount of Frenkel defects: these, indeed, can be considered as a source of interstitials that can migrate and evolve in larger aggregates. Due to the wide relaxation pattern induced by intrinsic interstitials, large supercells are necessary to avoid artifacts that, in practice, make first-principles calculations too computationally demanding, even for complexes involving just three interstitials. Following previous papers on di-interstitials, this paper reports on the structural, stability, and electronic properties of I-3 complexes, depending on the topology and the stoichiometry, approached by semiempirical tight-binding molecular dynamics and damped dynamics. I-3 complexes reveal a strong tendency to form these structures, and a stability hierarchy is determined between them. All the stable and metastable structures have been studied regarding the electronic structure, the charge distribution through the Mulliken analysis, the localization of the defect related wave function, and the local lattice strain field around the complex. The present study is aimed to define the selection rules that must be considered in order to build up larger I-n (with n >= 4) self-interstitials complexes in GaAs.