Optical properties of Si/Si:Er multi-nanolayer structures grown by SMBE method

Among Er-doped crystalline Si materials, Si/Si:Er multi-nanolayer structures grown by sublimation molecular beam epitaxy (SMBE) technique present extraordinary optical properties, with a narrow linewidth of the Er-related emission at 1.5 μm. Based on spectral analysis, the splitting of the ground state of Er³⁺ ions and the presence of only a single type of Er-related optical center, labeled Er-1, have been conclusively established. In this contribution, we briefly summarize some of the unique optical properties of Si/Si:Er multi-nanolayer structures: preferential formation of the Er-1 center and its microscopic structure, level of optical activity of Er, and relations with a donor level as well as with oxygen co-doping. Then we report on the most recent results on optical gain in Si/Si:Er multi-nanolayers. From variable stripe-length (VSL) and shifted excitation spot (SES) experiments, we estimated maximum gain cross section of Er-1 in the multi-nanolayer structure at about σ~10⁻¹⁷ cm². We also evaluate the magnitude of induced absorption by free carriers, and show that it precludes observation of the net optical gain.