Nucleation of two-dimensional islands on Si (111) during high-temperature epitaxial growth

The process of two-dimensional island nucleation at the surface of ultra large Si (111) during hightemperature epitaxial growth is studied by in situ ultrahigh-vacuum reflection electron microscopy. The critical terrace size $(D_{\operatorname{crit}})$, at which a two-dimensional island is nucleated in the center, is measured in the temperature range 900–1180$^\circ$C at different silicon fluxes onto the surface. It is found that the parameter $D_{\operatorname{crit}}^2$ is a power function of the frequency of island nucleation, with the exponent $\chi=(0.9\pm0.05)$ in the entire temperature range under study. It is established that the kinetics of nucleus formation is defined by the diffusion of adsorbed silicon atoms at temperatures of up to 1180$^\circ$C and the minimum critical nucleus size corresponds to 12 silicon atoms.