Combination of ultrafast time-resolved spectroscopy techniques for the analysis of electron dynamics of heliumlike impurity centers in silicon

We have combined ultrafast time-resolved techniques, available at European infrared free-electron laser facilities (HFML-FELIX and ELBE), for the analysis of intracenter relaxation processes in an atomiclike energy spectrum of the double donor magnesium in silicon. We show that complementary techniques enable the accurate analysis of complex transients inherent to strongly absorbing multilevel media. From the combined analysis of degenerate pump-probe, photon echo, and transient grating spectroscopy, we find short decay times of (10 +/- 1) ps and (30 +/- 3) ps for the 2p0 and 2p +/- states, respectively. These high decay rates exceed those obtained earlier for the shallow, one-electron donors in silicon, where intracenter relaxation profits from interaction with a single phonon of a host lattice.