  We report the observation of the quantum-confined Stark effect in Ge/SiGe
multiple quantum well heterostructures grown on Si(0.22)Ge(0.78) virtual
substrates. The large compressive strain in the Ge quantum well layers caused
by the lattice mismatch with the virtual substrate results in a blue shift of
the direct absorption edge, as well as a reduction in the \Gamma-valley
scattering lifetime because of strain-induced splittings of the conduction band
valleys. We investigate theoretically the \Gamma-valley carrier lifetimes by
evaluating the \Gamma-to-L and \Gamma-to-\Delta{} scattering rates in strained
Ge/SiGe semiconductor heterostructures. These scattering rates are used to
determine the lifetime broadening of excitonic peaks and the indirect
absorption in simulated absorption spectra, which are compared with measured
absorption spectra for quantum well structures with systematically-varied
dimensions. We find that \Gamma-to-\Delta{} scattering is significant in
compressively strained Ge quantum wells and that the \Gamma-valley electron
lifetime is less than 50 fs in the highly-strained structures reported here,
where \Gamma-to-\Delta{} scattering accounted for approximately half of the
total scattering rate.
