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

摘要

Raman scattering experiments were carried out on Si/SiGe heterostructures. The strain in both the top Si layer, and the Si_(1-x)Ge_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-x)Ge-x buffer layers with composition x < 0.35.