Observation of graded interfaces in strained View the MathML source layers (0.17 < x < 0.23) using photoreflectance

Photoreflectance has been used to study critical points along the (111) direction of View the MathML source (0.17 ≤ x ≤ 0.23) layers with SiGe layer widths between 30 Å and 105 Å. Transition energies of the SiGe E1 and View the MathML source critic points, found from fits with third derivative functions, increase with decreasing well width. The fitted energies are compared with energies deduced from composition profiles of the SiGe layer showing graded SiGe interfaces. These energies agree well with experiment for SiGe layer thickness > 50 Å, and so for these thicknesses the energy shifts can be explained by composition grading of the SiGe interfaces. For SiGe layers < 50 Å, the energy shifts can be explained in terms of composition grading and quantum confinement.