In situ REM observations of surfactant-mediated epitaxy: Growth of Ge on Si(111) surfaces mediated by Bi

A study of growth of Ge on Si(111) surfaces mediated by Bi was carried out by reflection electron microscopy and reflection high-energy electron diffraction (REM-RHEED). A study of Bi-adsorbed Si(111) surfaces was also carried out. A ''7 x 7'' structure was formed by deposition of Bi below 200 degrees C and it transformed into a (root x root 3)-beta structure at 200 degrees C. Dark particles appeared on the surface at 200 degrees C and the formation of the dark particles is the precursor of the formation of the (root 3 x root 3)-beta structure. The (root 3 x root 3)-beta structure transformed into a (root 3 x root 3)-alpha structure at 280 degrees C and domain contrast was seen on the (root 3 x root 3)-beta surface terraces. The density of three-dimensional (3D) islands of Ge on the Si(111)-Bi surfaces was higher and their size was smaller than those on the Si(111)(7 x 7) surfaces. Moreover, the critical thickness at which the layer growth of Ge transforms into the island growth on the surfaces with Bi was thinner than that on the bare surfaces. Smoothing of Ge films on the surfaces with Bi was observed.