sizes of the polycrystalline si 11 range from about 1 5 nm to 15 nm the thickness of the polycrystalline si 11 layer is typically between about 2 nm and 15 nm the described cvd si deposition process yields selective si deposition over exposed ge regions irrespective whether such regions are of a single crystal material or essentially of a polycrystalline material the process of selective polycrystalline si 11 formation over the polycrystalline ge 10 layer as shown in fig2 and in the junction void of fig1 b yields a third surface the difference between the second surface and the third surface is that now the first region is occupied by the polycrystalline si 11 instead of the polycrystalline ge 10 the deposition of polycrystalline ge over si and the deposition of polycrystalline si over ge has been experimentally confirmed using an atomic force microscopy afm in a technique known by the art in building up a sige polycrystalline layer of the desired thickness one is repeating the steps of the si deposition onto the second surface and the ge deposition onto the third surface as many times as needed the thin alternating layers of polycrystalline ge 10 and si 11 give the desired junction properties for mosfet device fabrication such as high conductivity and high dopant diffusion during the process of alternating between ge and si deposition in a an exemplary embodiment one can also deposit a thin porous oxygen containing layer 20 in the initial period of the si layer growth this.