Nonius approach for Si1-xGex/Si(001) epitaxy characterization

In Si(0 0 1)\(Si1-xGex 6-8 nm + Si 100-120 nm) x 2 (0.07 < x < 0.21) structures, grown by MBE on dislocation -free substrates and considered as nonius systems, X-ray reflectometry and diffraction on the reflection (004) revealed second period thickness decreasing compared to the first one due to misfit energy increasing. Electron microscopy of the same samples confirms the smaller thickness of the second period. Three-waves diffraction on the forbidden reflection (002) was applied to compare the structural perfection in two azimuthal directions (110): along the maximum substrate misorientation from the plane (001) and in the perpendicular direction. In the same sample with reduced photoluminescence quantum yield, it was found that the average period value determined by reflectometry (109.5 nm) was larger than that determined by diffraction on the reflection (004) (97.5 nm), and the angular distance between satellites on curves (002) corresponded to two different period values: 109.5 nm and 102 nm. Misfit dislocations are absent in the studied samples. This suggests both possible appearance of noncrystallographic defects in strained epitaxial layers and only effective thickness values cor-responding to perfect structure fragments which are determined by X-ray diffraction.