Growth of germanium on porous silicon (001)

The surface morphology of Ge grown on Si (001) and porous Si(001) by molecular beam epitaxy at 380°C is examined using atomic force microscopy (AFM). For layer thicknesses of 30 nm, the surface shows islanding while still maintaining some of the underlying roughness of the surface of porous Si. For thicknesses in the 100 nm range, the surface roughness is not visible, but the islanding persists. Unlike the case of silicon where islands tend to merge and nearly disappear as the thickness of the deposited layer rises, we observed on the porous layer the persistence of the islands with no merging even for macroscopic thicknesses as large as 0.73 microns.