Molecular dynamics simulations of growth and etching reactions on silicon surfaces

Molecular dynamics (MD) simulations are employed to study molecular-beam epitaxy (MBE) of Si and Ge thin films on the (2×1) dimer reconstructed surface of Si{100} and F atom reaction with the same surface. We have observed in the calculations mechanisms of dimer openings that lead to epitaxial growth. The results reveal a novel mechanism of collective dimer openings in which diffusing adatoms move perpendicular to the direction of the dimer rows on the original surface. The resulting relaxation of the dimer atoms and the underneath substate causes the opening of successive dimers along the way. This is in agreement with recent scanning tunneling microscope (STM) studies which show that the epitaxial layer grow preferentially in a direction perpendicular to the original dimer rows on the surface. The etching of silicon proceeds facilely by the addition of F atoms to the surface. The sticking probability of near thermal fluorine atoms on the reconstructed Si{100}-(2×1) surface as a function of F coverage is calculated. The sticking probability on the clean Si surface is not unity, and it decreases to approximately zero for fully fluorinated surface.