Terahertz-assisted excitation of the 1.5-mu m photoluminescence of Er in crystalline Si

Abstract

We show that the 1.5-mum emission from Si:Er generated by continuous-mode band-to-band optical excitation can be dramatically enhanced by terahertz radiation from a free-electron laser. The effect is observed at cryogenic temperatures in samples prepared from FZ-Si by high-temperature implantation with Er ions and requires a high density of infrared photons (hOmegaapproximate to100 meV). Based on experimental characteristics of this effect, we argue that the excitation mechanism responsible for the enhancement is, in this case, different from the previously discussed free-electron-laser-induced optical ionization of trapped carriers. A theoretical model of the energy transfer path is developed. It involves participation of a higher-lying conduction c2 band of the Si host and excitation into the I-4(11/2) second excited state of Er3+ ion. Since formation of the Er-related level is not necessary in this mechanism, it opens a possibility to excite a large fraction of Er3+ ions, including also these which are not linked to a recombination level in the band gap. Possible implications of the proposed model toward realization of a true three-level scheme in Si:Er are pointed out. Finally, further experiments necessary for testing and confirmation of the theoretically developed model are proposed.