Tracking recombination processes in Si:Er with a free-electron laser

Two-color optical spectroscopy is used to directly manipulate shallow levels available in Si:Er samples of different parameters. It is shown that Er photoluminescence can be quenched with a free-electron laser pulse applied shortly after the band-to-band excitation. For longer delay times between the visible and the infrared pulses an enhancenment of Er photoluminescence is observed. The effect is explained by the energy storage due to trapping of the photo generated carriers at shallow centers. These are subsequently ionized by the infrared beam and their recombination energy is transferred to the 4f-electron core of the Er3+ ion. In that way Er-related luminescence at 1.5 um can be generated by an infrared pulse applied within several milliseconds after the band-to-band excitation. By scanning the wavelength of the free-electron laser ionization spectra of the shallow centers participating in the energy storage are obtained providing their fingerprint. Presented results convincingly demonstrate power of the free-electron laser as a novel tool for spectroscopic applications in materials science of silicon. 2000 Elsevier Science B.V. All rights reserved