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Aiming at the precise profile control of Si1-x Ge x , selective epitaxial growth (SEG) conditions and Si1-x Ge x growth were investigated by ultrahigh-vacuum chemical vapor deposition (UHV-CVD) using Si2H6 and GeH4. As long as the total amount of Si2H6 did not exceed the critical amount, Si- and Si1-x Ge x -SEG were both achieved independent of source gas flow rate and substrate temperature. The Ge fraction x of Si1-x Ge x could be decided by the flow rate ratio between Si2H6 and GeH4, independent of substrate temperature. Fast gas flow switching realized the formation of a Si(120 Å)/Si1-x Ge x (69 Å) strained layer superlattice at 587°C.

The limiting conditions are presented of selective epitaxial growth (SEG) on a SiO2-patterned Si (001) substrate for Si gas-source molecular-beam epitaxy by use of 100% Si2H6. In the initial stage of growth, epitaxial Si was selectively grown on a Si surface in the wide temperature range of 500–850 °C. On the other hand, polycrystalline Si nucleation on a SiO2 surface was intimately related to the total volume of supply gas. At a substrate temperature of 700 °C and a Si2H6 flow rate of 60 sccm, a SEG layer could be deposited at a rate as high as 645 Å/min.

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