Comparison between surfactant-mediated Bi/Ge/Si(1 1 1) epitaxy and Ge/Si(1 1 1) epitaxy

Using scanning tunneling microscopy (STM) the Ge epitaxy on a Bi terminated Si(1 1 1) surface is compared to the growth without surfactant. During the growth of the Ge wetting layer in surfactant mediated epitaxy (SME), Si and Ge can be distinguished by different apparent heights in the STM images due to the Bi termination of the surface. As soon as the two bilayer high wetting layer is completed, Ge islands with a flat top and an underlying dislocation network occur. Elastic distortions due to the dislocation network result in periodic sub-angstrom height undulations measured by the STM. In this case the Ge islands have the form of a mesa. With increasing Ge coverage, these mesas spread laterally. Beyond a Ge coverage of 10 bilayers, the Ge mesas have coalesced and further Ge deposition leads to a 2D layer-by-layer growth of Ge on Si(1 1 1). In epitaxy without the use of a surfactant as well, the formation of Ge islands with an underlying dislocation network is observed. However, in this case the Ge islands are much higher and show no tendency to coalesce. The partially relaxed islands coexist with another type of tall islands.