Confinement effects in solid phase recrystallization of silicon nanowires

There are several routes to produce advanced nanowire transistors based on silicon. In order to obtain the desired electrical properties doping of the nanowires is required. Ion implantation is one of the favored methods to introduce dopant atoms in a controlled manner. If relatively high ion fluences are needed the originally single-crystalline nanowire is amorphized. Subsequently, thermal processing must be used to restore the silicon crystal and to activate the dopants electrically. In planar structures a complete restoration can be achieved by solid-phase epitaxial recrystallization, whereas more complex processes take place in the nanowires, due to the significant influence of surfaces and interfaces. It is highly desirable to understand the recrystallization in such confined systems on the atomic level. This work presents results of molecular dynamics simulations of solid phase recrystallization of silicon nanowires. It is shown that for embedded and free nanowires the recrystallization rate is significantly modified compared to the planar solid phase epitaxy. In general the original crystal cannot be restored completely. In dependence on whether embedded or free nanowires are investigated several phenomena are observed, such as stacking fault and twin formation, random nucleation of separate crystalline grains, as well as edge rounding and necking. The simulation results are in qualitative agreement with experimental findings.