Mid-infrared spectroscopy of the Er-related donor state in Si/Si:Er3+ nanolayers

We present experimental evidence on the donor level related to optical properties of the Er3+ ion in crystalline silicon. Using two-color spectroscopy with a free-electron laser we provide a direct link between the identified level in the bandgap and the optical properties of Er3+. The investigation is performed in sublimation MBE-grown Si/Si:Er multinanolayer structure, which allows us to take advantage of the preferential formation of a single Er-related center. Quenching of the Er-related 1.5 μm photoluminescence, due to ionization of the donor state with energy ED ≈ 225 meV, is demonstrated. A microscopic model of the PL quenching mechanism as Auger type energy transfer between excited Er3+ ions and free carriers optically ionized from the Er-related donor states is put forward.