Adsorption and diffusion dynamics of a Ge adatom on the Si{100}(2 x 1) surface.

Abstract

The Ge-adatom adsorption and diffusion on the fully relaxed Si{100}(2\ifmmode\times\else\texttimes\fi{}1) surface is studied by a combination of molecular-dynamics simulations with Tersoff's potential for the Ge-Si interactions, a simplified transition-state theory of Voter and lattice-gas simulations. Six local minima for adsorption are found on the surface, and the activation energies between each are determined. The macroscopic diffusion follows the Arrhenius behavior with D=4.3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ exp(-0.73 eV/kT) ${\mathrm{cm}}^{2}$/sec. In addition, we find that the adatom diffusion is anisotropic in nature and the direction of easy diffusion is perpendicular to the dimers (i.e., parallel to the dimer rows) of the original surface. A comparison with the Si-adatom diffusion shows that the Ge-adatom diffusion is less anisotropic and that Ge adatoms diffuse 2--3 times more slowly than Si adatoms on the same surface. The diffusion coefficients for Ge- and Si-adatom migrations perpendicular to the dimer rows are found to be ${\mathit{D}}_{\mathrm{\ensuremath{\perp}}}^{\mathrm{Ge}}$=2.8\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ exp(-1.17 eV/kT) ${\mathrm{cm}}^{2}$/sec and ${\mathit{D}}_{\mathrm{\ensuremath{\perp}}}^{\mathrm{Si}}$=4.8\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ exp(-1.20 eV/kT) ${\mathrm{cm}}^{2}$/sec, respectively.