The excess charge carrier lifetimes in Ge layers grown on Si or germanium-on-insulator are
measured by synchrotron based pump-probe transmission spectroscopy. We observe that
the lifetimes do not strongly depend on growth parameters and annealing procedure, but on
the doping profile. The defect layer at the Ge/Si interface is found to be the main non-
radiative recombination channel. Therefore, the longest lifetimes in Ge/Si (2.6 ns) are
achieved in sufficiently thick Ge layers with a built-in field, which repels electrons from the …