Mechanism of inward oxygen diffusion on H-, OH-, and nonterminated silicon surfaces

Abstract

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: oxygen diffusions at an (i) H-terminated, (ii) OH-terminated, and (iii) nonterminated surface. The activation energies required for oxygen diffusion at the nonterminated Si surfaces were estimated to be $1.6 \mathrm{eV},$ which are fairly small compared to oxygen diffusion inside a Si crystal $(2.5 \mathrm{eV}$ in experiment and $2.7 \mathrm{eV}$ in theory [Phys. Rev. Lett. 84, 4633 $(2000)]).$ On the other hand, the activation energies required for oxygen diffusion at H- and OH-terminated surfaces were estimated to be $3.7$ and $3.5 \mathrm{eV},$ which are larger than that for the inside of a crystal. The activation energy largely depends on dangling bonds and geometrical strain at the surface. The electron distribution was also surveyed to clarify which kinds of bond formation dominate the diffusion reactions.