We analyze transient processes during oxygen bombardment and sputtering of epitaxial SixGe1-x layers with different compositions (0 < x < 0.75). We show that a composition-dependent drop of the Ge+ secondary ion yield extends the transient period as a function of bombardment conditions. By means of computer modeling we describe secondary ion emission kinetics and simulate the dynamics of structural and compositional changes, including the Ge+ intensity drop. An interfacial transient period after crossing a Si/SixGe1-x interface can be neglected, if the altered layer formation is completed within the Si cap layer. This allows reliable quantification of dopant spikes within a few nm to these interfaces. (C) 2002 Published by Elsevier Science B.V.