Strain engineering via amorphization and recrystallization in Si/Ge heterostructures

Abstract

We use molecular dynamics with the reactive potential ReaxFF to study strain relaxation during the amorphization and recrystallization of silicon-germanium epitaxial nanolaminates. Starting with a coherent heterostructure with (010) Si/Ge interfaces and 3D periodic boundary conditions, we use local heating and quenching to amorphize half of the simulation cell with crystal-amorphous interfaces normal to [001]. We find strain relaxation along [001] as the crystalline Ge section expands into the amorphous material and crystalline Si contracts from it. The amount of strain relaxation correlates with the atomic transport from the amorphized Ge to Si section and increases as the periodic width of the crystalline-amorphous pattern decreases and the height of the Si/Ge bilayer increases. Recrystallization leads to a decrease in strain relaxation; however, structures with low aspect ratio retain a significant fraction of the strain relaxation. Interestingly, this remnant strain relaxation is not due to misfit dislocations but originates in clusters of lattice defects located on either side of the interface and caused by atomic transport. Our results show that local amorphization followed by recrystallization is a possible avenue for strain engineering in semiconductor heterostructures.