Ge segregation at Si/Si1−<i>x</i>Ge<i>x</i> interfaces grown by molecular beam epitaxy

The interface quality of Si/Si1−xGex (0.08≤x≤0.33) interfaces grown by molecular beam epitaxy has been studied by means of secondary-ion mass spectrometry. Ge segregation occurs into the Si capping layers. The segregation is characterized by a 17 nm/dec slope; the total amount of segregated Ge corresponds to a few tenths of a monolayer. The phenomenon is independent of the Ge fraction and does not depend on temperature as long as crystal growth is perfect. A possible explanation is given in terms of a Ge adlayer that is formed during growth as a result of site exchange between subsurface Ge and surface Si atoms. This adlayer is incorporated slowly during further Si growth. The Ge segregation can be suppressed by having an adlayer of Ga on the surface of the growing structure.