H segregation by adatoms on hydrogen-terminated semiconductor surfaces

We present our first-principles total-energy calculation of the adsorption of various adatoms (the third-row elements and 3d transition metals) and the segregation of H on the hydrogen-terminated Si(111) and Ge(111) surfaces [H/Si(111) and H/Ge(111)]. We find out that the adsorption structures are closely related with the number of the partially-filled valence electrons, n. The Mg and Zn adatoms with filled valence electrons (n = 0) do not interact with the H-terminated surfaces. The adatoms with n = 1, such as Na, Al, Cu and Ag, interact weakly with the surfaces. On the other hand, elements with n ≥ 2, such as group IV ∼ VI and transition metals, show a strong chemical interaction with the surfaces. In these cases, one or more H atoms are segregated from the surface without any energy barrier.