Raman investigation of strain in Si/SiGe heterostructures: Precise determination of the strain-shift coefficient of Si bands

Raman scattering experiments were carried out on Si/SiGe heterostructures. The strain in both the top Si layer, and the Si_1-xGe_x buffer layers with various Ge compositions was evaluated using several excitation sources, together with x-ray diffraction and secondary ion mass spectrometry. The strain-shift coefficient, which is a necessary quantity to evaluate the strain by Raman spectroscopy, was precisely determined. The dependence of the Si–Si band frequency on the Ge composition in the SiGe alloy was also examined. We found that the strained top-Si layers with a thickness below 25 nm experience coherent growth on Si_1-xGe_x buffer layers with composition x≪0.35.