Growth mechanisms in GeÕSi„111... heteroepitaxy with and without Bi as a surfactant

We compare the initial stages of growth of Ge on Si~111! with Bi as a surfactant and without surfactant. At the beginning of growth, three-dimensional islands with a strain relieving dislocation network at their base are formed in both growth systems. These islands can be regarded as seeds of a flat relaxed Ge layer on Si~111!. However, such Ge layer forms at later stages of growth only in the growth with Bi surfactant, while the growing Ge layer without surfactant remains rough. What makes the difference and the success of Bi surfactant mediated epitaxy is the lateral growth and coalescence of the seed islands that cover the entire surface within first 15 bilayers of Ge deposition. This happens due to a kinetic limitation of the incorporation of Ge into the growing layer in the presence of surfactant.