Abstract
Ge/SiGe strained-layer heterostructures have been investigated using photoreflectance (PR) spectroscopy. On the basis of the comparison between the experimental and calculated quantum well-related transition energies formed at the Γ point, band discontinuities at the Ge/SiGe heterojunction are determined and found to vary linearly with Ge content in the SiGe layer. Conduction band offset ratio Q c (= ΔE c/(ΔE c+ΔE v HH )) at the Γ point is evaluated to be 0.68 ±0.08 . From the intrinsic linewidth of the quantum well-related transitions, roughness at the Ge/SiGe heterointerface has been characterized for the first time and is estimated to be ±1 monolayer (ML). In addition, the splittings in the PR spectra are observed in some samples at low temperatures. These splittings are due to the difference in the well width and correspond to the height (or depth) of about 10 ML.