A STUDY ON EXCITATION AND DE-EXCITATION MECHANISMS OF HIGHLYRARE-EARTH MATERIAL-DOPED SILICON THIN FILMS

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The objective of this research is to understand the excitation and de-excitation mechanisms of highly Er-doped Si (Si : Er) thin films. Er doping into Si thin films has been carried out by the laser ablation technique that is able to control easily the Er density over 10ィイD119ィエD1 to 10ィイD121ィエD1 cmィイD1-3ィエD1. The photo-lumeinescence for cw and pulse excitations has been achieved at the temperature range from 20K to room temperature. Intense 1.54 μm-emission originating from intra-4f shell transitions in ErィイD13+ィエD1 ions has been observed even at room temperature. The increase of Er density over two orders of magnitude can not immediately result in a linear increase in ErィイD13+ィエD1-emission intensity. The time response measurement indicated that the change in the rise time of ErィイD13+ィエD1-emission directly shows that ErィイD13+ィエD1 ions are excited indirectly by the energy transfer associated with the recombination of electron-hole pairs generated optically in Si host. From the analysis of time response measurement on the basis of the energy transfer, it was found that the decrease of the excitation efficiency of ErィイD13+ィエD1 ions was responsible for the suppression of ErィイD13+ィエD1-emission intensity in highly Er-doped Si films. The local structure of the Si : Er films has been investigated by the combined analysis of the extended x-ray absorption fine structure measurement and the x-ray absorption structure simulation based on the multiple-scattering theory. This result concludes that dominant local structure of optically active Er centers is sixfold bonding to neighboring oxygen atoms, that is, a CィイD24VィエD2 symmetry.