Direct observation of the two-stage excitation mechanism of Er in Si

In Er-doped silicon we have found direct evidence for the formation of the Er-related intermediate state that is a precursor of the final 4f-electron excited state responsible for the 0.8 eV luminescence. Time-resolved photoluminescence following band-gap illumination shows disruption of this center by a THz pulse from a free-electron laser. The decay of the intermediate state could be directly monitored in this double-beam experiment and a lifetime of approximately 100 µs has been found. In this way the most characteristic step in the excitation mechanism of the Er ion in silicon has been revealed experimentally.