Ge islands on Si(111) at coverages near the transition from two-dimensional to three-dimensional growth

Abstract

We use scanning reflection electron microscopy (SREM) to study three-dimensional Ge island formation on the Si(111) surface at coverages near the transition from two-dimensional to three-dimensional growth under Ge fluxes between 0.001 and 0.02 BL/s and at temperatures between 380 and 690°C. The SREM images clearly show that the formation of flat three-dimensional islands with large lateral dimensions is dominant at higher temperatures. An average critical island size of about nine atoms was obtained from the flux dependence of island density. The existence of such large size critical islands is supported by the intermediate formation of the second Ge bilayer before island nucleation, which then decomposes, and by the rapid saturation of island density. From the temperature dependence of island density the activation energy for a Ge atom to detach from the islands to form an adatom was estimated to be ∼1.1 eV.