Nucleation and step-flow growth in surfactant mediated homoepitaxy with exchange/de-exchange kinetics

The nucleation rate and the transition to step-flow growth are considered i n detail in the two limiting cases of surfactant mediated homoepitaxy: (i) reversible exchange of crystal and surfactant atoms (an exchange-de-exchang e equilibrium); (ii) irreversible exchange (fast exchange of the atoms upon striking the surface and absence of de-exchange). It is shown that in both cases the critical terrace width above which nucleation takes place displa ys an Arrhenius behavior as has been experimentally established by Iwanari and Takayanagi [J, Cryst. Growth 119 (1992) 229]. The square of the critica l terrace width for step-flow growth scales with the atom arrival rate, the scaling exponents being the same, which determines the scaling behavior of the island densities in the submonolayer regime of growth. It is shown tha t in the case of Sn mediated growth of Si(111) the surfactant drives the nu cleation process closer to the phase equilibrium, the critical nucleus is o ne order of magnitude larger than in the clean case, and the surfactant sti mulates the step-flow growth. (C) 1999 Elsevier Science B.V. All rights res erved.