Photoreflectance in Ge/Ge0.7Si0.3strained-layer superlattices

We report low-temperature (77 K) photoreflectance measurements in two Ge/${\mathrm{Ge}}_{0.7}$ ${\mathrm{Si}}_{0.3}$ strained-layer superlattices, in the photon energy range 0.8–1.8 eV. The multiple lines observed in our spectra in this energy region can be consistently explained in terms of quantum confinement of zone-center bulk Ge states. Quantitative agreement is obtained when energy-dependent masses are used for the electrons and light-hole states within a scalar three-band model. This interpretation leads to values of the average valence-band offsets in good agreement with previous ab initio theoretical calculations.