| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 92 === Semiconducting β-FeSi2 have attracted great attention in the recent decade. Because it has a direct band-gap of about 0.8eV, and it can emit a light of 1.55μm. With this property, silicon based IR-LED(Light emitting device) and IR-Sensor can be synthesized. But its optical property is still controversial, M. G. Grimaldi et al. suggested that the luminescence of β-FeSi2 precipitates is related to its location. So that our study is using a variety of annealing process to see if we can control the location of β-FeSi2 precipitates.
The general method of ion beam synthesized(IBS) β-FeSi2 precipitates is to heat target during ion implantation. After annealing at 830oC for 18 hours, β-FeSi2 will precipitate inside specimen. In our experiment, ion implantation will be carried out under room temperature. After annealing at 830oC for 18 hours, we can observe β-FeSi2 precipitates close to surface by TEM images. Because heating of target can avoid the amorphization of silicon substrate, and the diffusivity of Fe atom in amorphous silicon is larger than in crystal silicon.. This fact will result in diffusion of Fe atoms to surface before precipitation of β-FeSi2. In the next experiment, the low temperature solid phase epitaxy will be conducted before annealing at 830oC for 18 hours. Likewise, the location of β-FeSi2 precipitates will be observed.
We also synthesized β-FeSi2 precipitates by co-sputtering. Samples of IBS always produce defects like dislocation loops. Presentation of defects is also harmful to the luminescence of β-FeSi2 precipitates. Ion gun will be used to co-sputtering Fe-Si atoms onto Si(001) wafer. In order to avoid oxidation of Fe and Si atoms, a thickness of about 50nm Germanium layer will be capped on our sample. After different annealing process, the retardation of transformation of Fe silicide by presentation of Ge layer will be observed.
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