Self-interstitial–hydrogen complexes in Si

Native defects in Si are readily created during a variety of processes. They diffuse rapidly and interact with themselves, with each other, and with many impurities, in particular hydrogen. Vacancy-hydrogen complexes are better understood than self-interstitial--hydrogen ones, except for (one of) the I,H₂ complexes, which has been detected by infrared absorption spectroscopy and predicted theoretically. In this paper, the interactions between one neutral self-interstitial (I) and up to four hydrogen impurities are studied systematically using first-principles molecular-dynamics simulations with basis sets consisting of linear combinations of atomic orbitals. Except for $n=1,$ each of the I,Hₙ complexes has at least one metastable configuration. One family of structures has two H's bound to the same Si atom. Another family of structures has a single H bound to each Si atom, forming a ``zig-zag'' chain of Si-H bonds. The former complexes are more localized, with H tying up bonds at the defect itself. The latter complexes are more extended, and illustrate how H relieves the lattice strain associated with a defect. The experimentally observed I,H₂ complex is the most stable of the series. The configurations, stabilities, electrical activity, and spin densities are discussed. We find that total energy differences and electronic structures are sensitive to the →k-point sampling, even when using 128 host-atoms cells. For the type of defects discussed here, more than four →k points may be needed to achieve convergence in that respect.