We have studied the structural properties of tensile-strained Si layers grown on polished Si 0.6 Ge 0.4 and Si 0.5 Ge 0.5 virtual substrates as a function of their thickness. Two gaseous precursor chemistries have been assessed for the reduced pressure-chemical vapour deposition of the sSi layers: SiH 2 Cl 2 at 700 • C and SiH 4 at 600 • C. We have used specular x-ray reflectivity and spectroscopic ellipsometry to gain access to the sSi layer thickness (and the associated sSi growth rate). The surfaces of sSi layers grown at 600 • C using SiH 4 are characterized by a small spatial wavelength (a few hundred nm) roughness. Meanwhile, some lines along the 1 1 0 directions can be observed for thick sSi layers grown at 700 • C using SiH 2 Cl 2 , hinting at the presence of stacking faults. We obtained (for 10 µm × 10 µm atomic force microscopy images) surface root-mean-square roughness (Z ranges) between 0.19 and 0.36 nm (1.8 and 3.9 nm). By comparison, the rms roughnesses (the Z range) associated with 360 µm × 368 µm optical interferometry images are between 0.7 and 1.4 nm (7.1 and 12.1 nm), with some small amplitude but very long spatial wavelength (tens of µm) surface cross-hatch remaining on Si 0.6 Ge 0.4 VS. The interfaces between sSi and SiGe are very abrupt, as illustrated by high-resolution transmission electron microscopy and by the Ge decay profile in secondary ions mass spectrometry: 0.73 nm/decade for sSi on Si 0.5 Ge 0.5 VS and 1.06 nm/decade for sSi on Si 0.6 Ge 0.4 VS, more or less independently of the sSi growth chemistry. The larger value for sSi on Si 0.6 Ge 0.4 VS is most probably due to some instrumental broadening linked to the small remaining cross-hatch.

We have studied the structural properties of tensile strained Si (sSi) layers grown on polished Si0.6Ge0.4 and Si0.5Ge0.5 virtual substrates as a function of their thickness. The surface morphology, the tensile strain, the linear density of defects, and the threading dislocation density have been quantified for different growth conditions and sSi layer thickness.