Diffusion mechanisms of an O atom at Si surfaces were investigated with cluster computations with the density-functional theory. Calculations were performed for three cases: O diffusions at an H-terminated, OH-terminated and non-terminated surface. The activation energies required for O diffusion at the non-terminated Si surfaces were estimated to be 1.6eV, which were fairly small compared to O diffusion inside a Si crystal (2.5eV in experiment and 2.7eV in theory). On the other hand, the activation energies required for O diffusion at H- and OH-terminated surfaces were estimated to be 3.7 and 3.5eV; which were larger than that for the inside of a crystal. The activation energy depended largely upon dangling bonds and geometrical strain at the surface. The electron distribution was also surveyed in order to clarify which kinds of bond formation dominate the diffusion reactions.

Mechanism of Inward Oxygen Diffusion on H-, OH-, and Non-Terminated Silicon Surfaces. T.Hoshino, Y.Nishioka: Physical Review B, 2001, 64[12], 125322 (6pp)