Diffusion of Ag adatom on the H-terminated and clean Si(111) surfaces: A first-principles study

Using a first-principles calculation method, we investigate the adsorption and diffusion of a Ag adatom on the H-terminated and clean Si(111) surface, which would be useful in understanding the initial stages of metal growth on semiconductor substrates. We perform extensive searches for metastable surface structures induced by the Ag adatom adsorption, and then find its diffusion barriers and pathways on both kinds of the substrates. The calculated barrier for the Ag atom on the H-terminated surface is only 0.14 eV. On the clean surface, the diffusion barriers inside a half-unit cell (HUC) and between HUC's are calculated at 0.27 and 0.88 eV, respectively. The present results provide a qualitative description of the Ag growth modes on the Si(111) surfaces: the three-dimensional island growth on the H-terminated surface and the formation of the wetting layer on the clean surface. In addition, the calculated barrier of 0.88 eV agrees well with the diffusion barrier measured by recent scanning-tunneling microscopy.