The growth kinetics and structural properties of nominally 15-45% SiGe virtual substrates (VS) on Si(100), Si(110) or Si(111) substrates have been investigated. Our "best" (100) growth procedure has been used, which leads to the formation of high-quality SiGe(100) VS with threading dislocation densities around 10(5) cm(-2). The mean SiGe growth rate (GR) on (100) is higher than the one on (111), which is itself higher than the one on (110) (more precisely: GR(110) similar to 0.6 x GR(100) and GR(111) similar to 0.85 x GR(100)). The trend is the opposite one for the mean Ge content, with %Ge x 1.5 and x 1.2 higher on (110) and (111) than on (100), respectively. The Ge concentration dependence on mass-flow ratio has been quantified using a x(Ge)/(1-x(Ge))=p(F(GeH4)/F(SiH2Cl2)) relationship for all surface orientations. We have obtained (110) and (111) p values 1.8-2.0 and 1.3-1.5 times higher than on (100). We have otherwise studied the structural properties of SiGe(100), (110) and (111) VS. Original surface morphologies have been evidenced for each surface orientation. Cross-hatch, "half cross-hatch" and triangular arrays have been observed on (100), (110) and (111), with respectively slight and strong surface roughening for the latter two orientations. Higher defect densities have been evidenced by TEM on SiGe(110) and (111) VS than on (100). Whereas stacking faults have propagated from the Si(111) substrate all the way up to the surface, these defects are mostly confined in the SiGe ramp when growing on (110), with a 0.5 mu m defect-free area on top. Threading dislocation densities (from Schimmel defect etching) are roughly equal to 10(8) cm(-2) on both Si0.72Ge0.28 (110) and Si0.80Ge0.20 (111) VS. Finally, SiGe VS are crystalline whatever the Si surface orientation as shown by the coherent X-ray diffraction profiles or reciprocal space maps obtained. SiGe(100) and (110) VS are both fully relaxed, whereas the (111) ones may be in a tensily strained configuration. (C) 2008 Elsevier BY. All rights reserved.