NUCLEATION BEHAVIOR DURING SILICON UHV-CVD ON SI(111)7 X 7

We report a UH V-CVD homoepitaxy study on the Si(111)7 x 7 surface inv estigated with Scanning Tunnelling Microscopy (STM). We have investiga ted the two-dimensional island density in the temperature range from 4 50 to 550 degrees C and silane pressure range from to 8 x 10(-4) Torr. Contrary to experiments using molecular beam epitaxy. we find that th e two-dimensional island density in UHV-CVD cannot be directly describ ed by the standard nucleation theory. We discuss this point and show t hat the variation of the steady-state hydrogen coverage on the surface during pressure- or temperature-dependent experiments can explain the observed two-dimensional island density behaviour. (C) 1998 Elsevier Science B.V.