Optical Characteristics Of Er-doped Al₂O₃/Si Multilayers

The 1.54μm emission from the intra-4f transition of Erbium ions has aroused great research interest in the application of optic-electric integration technology because that wavelength is just at the minimum loss window of fiber communication. Si nano-crystals (Si-NCs) sensitized Er3+ luminescence in SiO2-based systems hasbeen investigated systematically. Usually, a high annealing temperature about 900℃or higher is required to prepare Si-NCs. Although Al2O3 is also an excellent host for Er3+ luminescence, the sensitization of Si-NCs and the optimized conditions for Er3+ luminescence in Al2O3 were rarely investigated systematically.In this thesis, Er-doped Al2O3/Si multilayers with Si layer of various thicknesses were fabricated by pulsed laser deposition and the formation of Si-NCs and the optimized Er3+ lumininescence sensitizated by Si-NCs are both achieved at low. annealing temperatures. By comparing the onset temperatures of crystallization in the erbium-doped and un-doped samples, we found that a shallow implantation of Er into Si layers is achieved during the deposition process thanks to the presence of energetic Er species produced by PLD. The doped Er atoms induce additional strains in the amorphous Si layers and serve as nucleation centers to achieve the formation of Si-NCs at low annealing temperatures. The Raman scattering, X-Ray Diffraction and transmission electron microscopy measurements are used to characterize the microstructure of the samples and can give firm evidence of the formation of Si-NCs. Photoluminescence, PL excitation and time-resolved decay transient PL spectra were carried out to investigate the optical properties of Er-doped Al2O3/Si Multilayers. When Si-NCs are introduced as sensitizers in the multilayers, the PL of Er3+ is significantly enhanced. The maximum Er3+ luminescence intensity is achieved in the samples annealed at a relatively low temperature of about 600℃, where a high density of small Si-NCs and a good local environment of Er+ are advantageous, and then the intensity gradually decreases with the increase of the annealing temperature. The greatly decreased density of Si-NCs and poor sensitizing effect of large Si-NCs as well as the energy back transfer de-excitation process is mainly responsible for the quenching of Er3+ luminescence under high annealing temperatures. When the multilayers were covered by Ag films, the Er3+ luminescence is enhanced thanks to the effect of the surface plasmon polarization of Ag nano-islands. In addtion, MIS electro-luminescence devices based on the Er-doped Al2O3/Si films were fabricated, and the electro-luminescence at 1.54μm has been detected at room temperature. The present results reveal that achieving the enhanced formation of Si-NCs and optimized Er3+ luminescence at low annealing temperatures makes the structure a promising candidate for future low-cost Si-based optoelectronic devices.