The formation of silicon (111) boron surface phases and their influence on the epitaxial growth of silicon and germanium

We present results obtained by different analysis methods as scanning tunneling microscopy (STM), atomic force microscopy (AFM), grazing incidence small angle X-ray scattering (GISAXS), and elastic recoil detection (ERD) on two similar semiconductor structures grown by molecular beam epitaxy (1) Si(111) substrate/Si buffer layer/B layer with sigma(B) = (2.6 +/- delta) x 10(14) cm(-2)/Ge cap layer and (2) Si(111) substrate/Si buffer layer/B layer with sigma(B) = (2.6 +/- delta) x 10(14) cm(-2)/Si cap layer. It will be shown that the deposition of B with concentrations up to 2.6 x 10(14) cm(-2) leads to a breakdown of the 7 x 7 reconstructed Si surface of the buffer layer and the formation of a Si(111)-root 3 x root 3-R30 degrees B surface phase (BSP) located on T-4-sites. Furthermore it is shown that this BSP acts as a 'lubricant' for additional deposited adatoms (Si and Ge) at deposition temperatures <800 degrees C due to the saturation of all Si dangling bonds. This leads to the formation of triangular, nearly relaxed, and well ordered Ge dots in the special case of Ge deposited at 400 degrees C onto a BSP. For higher deposition temperatures it is shown that this 'lubricant effect' vanishes due to the B migration from the T-4-site via SS into the substrate. (C) 2000 Elsevier Science S.A. All rights reserved.