Ge adatom adsorption, diffusion, and exchange on surfactant-covered Si(111) surfaces

We investigate the effects of various surfactants on the Ge adsorption, dif fusion, and exchange on Si(111) surfaces through first-principles pseudopot ential total-energy calculations. For surfactant-covered surfaces such as S i(111):Ga-1 x 1, Si(111):As-1 x 1,and Si(111):Sb-(root 3 x root 3)R30 degre es, Ge adatoms are generally incorporated into the surfactant layer. On the Ga-covered surface, we find-strong interactions between the Ge and Ga atom s, which result in large activation energies for both Ge surface diffusion and exchange with an underlying Ga atom. In the case of As surfactants, the activation energies for adatom diffusion and exchange are much reduced bec ause of the weak couplings between the Ge and As atoms. Similarly, on the S b-covered surface, the exchange between the adatoms and surfactants takes p lace easily; however, the surface diffusion is severely suppressed due to a relatively large energy gain by the exchange process. [S0163-1829(99)00128 -9].