ADSORPTION AND DIFFUSION DYNAMICS OF A GE ADATOM ON THE SI(100)(2X1) SURFACE

The Ge-adatom adsorption and diffusion on the fully relaxed Si {100} (2 X 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 X 10(-4) exp(-0.73 eV/kT) cm2/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 D(perpendicular-to)Ge = 2.8 X10(-3) exp(-1.17 eV/kT) cm2/sec and D(perpendicular-to)Si = 4.8 X 10(-3) exp(-1.20eV/kT) cm2/sec, respectively.