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

Two-color optical spectroscopy is used to directly manipulate shallow level s available in Si:Er samples of different parameters. It is shown that Er p hotoluminescence can be quenched with a free-electron laser pulse applied s hortly after the band-to-band excitation. For longer delay times between th e visible and the infrared pulses an enhancenment of Er photoluminescence i s observed. The effect is explained by the energy storage due to trapping o f the photo generated carriers at shallow centers. These are subsequently i onized by the infrared beam and their recombination energy is transferred t o the 4f-electron core of the Er3+ ion. In that way Er-related luminescence at 1.5 mu m can be generated by an infrared pulse applied within several m illiseconds after the hand-to-band excitation. By scanning the wavelength o f the Free-electron laser ionization spectra of the shallow centers partici pating in the energy storage are obtained providing their fingerprint. Pres ented results convincingly demonstrate Fewer of the free-electron laser as a novel tool for spectroscopic applications in materials science of silicon . (C) 2000 Elsevier Science B.V. All rights reserved.