Characterization of Ge/SiGe strained-barrier quantum-well structures using photoreflectance spectroscopy

We have investigated Ge/SiGe strained-barrier quantum-well structures using photoreflectance spectroscopy. On the basis of the Γ-point transition energies associated with the Ge quantum well, the band offset at the heterojunction between Ge and SiGe has been found to vary linearly with the germanium composition in the SiGe barrier layer. The conduction-band-offset ratio ${\mathit{Q}}_{\mathit{c}}$[=Δ${\mathit{E}}_{\mathit{c}}$/(Δ${\mathit{E}}_{\mathit{c}}$+Δ${\mathit{E}}_{\mathrm{vh}}$)] at the Γ point is estimated to be 0.68±0.08. From the intrinsic linewidth of the quantum-well-related transitions, interface roughness has been characterized in this system and is estimated to be ±1 monolayer in our samples.