Spectroscopic probing of defect-related energy storage in silicon doped with erbium

An enhancement of 1.5 mu m Si : Er photoluminescence by a mid-infrared pulse from a free-electron laser is investigated in detail. It is concluded that the effect is a consequence of defect-related energy storage in Si : Er samples. Carriers generated by a band-to-band excitation are participating not only in the excitation of Er luminescence via the excitonic mechanism, but are also trapped at various defect states. The infrared pulse photoionizes them, thus promoting extra carriers into the excitation channel of the Er(3+) ion and leading to an additional luminescence. By scanning the wavelength of the free-electron laser ionization spectra of shallow centers participating in the energy transfer are obtained. The results also elucidate a special role of oxygen in Si : Er luminescence. (C) 1999 Elsevier Science B.V. All rights reserved.