Modification of growth kinetics in surfactant-mediated epitaxy.

Abstract

The influence of Sb, As, Ga, and In as surfactants on the Si/Si(111) homoepitaxy is studied using scanning tunneling microscopy. The nucleation of two-dimensional (2D) Si islands on the surfactant-terminated surface was studied as a function of temperature. The island densities and depleted zones show Arrhenius behavior. Surfactants modify the Si epitaxy in quite a different way. Indium as surfactant increases the diffusivity of the Si atoms, whereas Sb and As drastically decrease the diffusion length of Si. When we apply these results to Ge epitaxy on Si the reduction of the diffusion length is shown to be essential for the suppression of 3D islanding in surfactant-mediated Ge/Si heteroepitaxy. Generally, elements of group III and IV as surfactants that enhance the diffusivity in Si homoepitaxy lead to 3D islanding in Ge/Si heteroepitaxy. Elements of group V and VI reduce the diffusion length in Si homoepitaxy and give rise to a suppression of 3D islanding in Ge/Si heteroepitaxy. The temperature dependence and rate dependence of the nucleation of 2D islands in Si/Si(111) homoepitaxy can be described in the framework of classical nucleation theories yielding a critical nucleus size of 6 and an activation energy of diffusion of 0.75 eV. Experimentally no indication for a reflective potential barrier for step-down motion of diffusing Si atoms (Ehrlich-Schwoebel barrier) was found.