The ultrafast carrier dynamics of Ge/SiGe quantum wells on Si substrate is investigated by pump-probe spectroscopy. Spectrally tunable 80 fs pulses emitted by an opto-parametric amplifier are used to excite the sample and a white-light supercontinuum generated from a 1 kHz Ti:sapphire regenerative amplifier system is used to probe the sample transmission.
Pronounced nonequilibrium effects are observed in the relaxation dynamics. The pump energy dependence of these effects is discussed. If the sample is excited under close-to-resonant pumping conditions, transient gain is observed. The findings are explained using a microscopic many-body theory. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)