Theoretical study of hydrogen stability and aggregation in dislocation cores in silicon

Abstract

The interaction between hydrogen and a dislocation in silicon has been investigated using first-principles calculation. We consider $30\ifmmode^\circ\else\textdegree\fi{}$ and $90\ifmmode^\circ\else\textdegree\fi{}$ partial dislocations with both single and double periodic structures and nondissociated screw dislocation starting from the case of one single H to a fully H-filled dislocation line. In the case of a single H atom, H is preferentially located in a bond-centered-like site after a possible breaking of a Si--Si bond. In case of two H atoms, the molecular ${\text{H}}_{2}$ can be stable but is never the lowest energy configuration. If initially located in a bond-centered site, ${\text{H}}_{2}$ usually spontaneously dissociates into two H atoms and breaks the Si--Si bond followed by the passivation of resulting dangling bonds by H atoms. When additional H atoms are inserted into partial dislocation cores, they first induce the breaking of the largely strained Si--Si bonds in the dislocation core, then passivate the created dangling bonds. Next the insertion of stable ${\text{H}}_{2}$ near the dislocation core becomes favorable. A maximum H density is determined as 6 H atoms per length of Burgers vector and the largest energy gain in energy is obtained for a $90\ifmmode^\circ\else\textdegree\fi{}$ single periodic partial dislocation. Our calculations also suggest that the presence of few hydrogens could have a non-negligible influence on the dislocation structures, inducing core reconstructions. The mobility of H along the dislocation line is briefly addressed in the case of the $90\ifmmode^\circ\else\textdegree\fi{}$ single periodic partial dislocation core.