Excitation Mechanism of Er Photoluminescence in Bulk Si And SiO₂ With Nanocrystals

Abstract

For about one decade, Er doped Si attracted the attention of researchers with the aim to apply it to integrated silicon-based optoelectronic devices. In fact, Er emission falls into the band of minimum absorption losses of silica glass optical fibers used in telecommunications. The advantage of Er-doped Si consists in the possibility to increase significantly the effective cross section of excitation of the rare earth ions [1]. This enhancement is due to a strong band-to-band absorption of the pumping light in a wide spectral range followed by an Auger process in which electron-hole pairs recombine with the transfer of energy to the 4f-shell of Er. The excess energy is taken by free electrons or phonons. However, Er luminescence in a matrix of crystalline Si is characterized by a strong temperature quenching and can be hardly observed above 200 K. Temperature quenching is caused by the thermally activated de-excitation of Er resulting from reverse Auger process accompanied by energy back transfer. Therefore, the optical medium which favors the excitation of rare earth ions is not adequate as what concerns the emission process.