| 研究実績の概要 |
The aim of this study is to perform fundamental and applied studies on porous nano-silicon, nano-silicon oxide, plasmonic nano-metal-silicon composite layers, and powders, for the control of nano-structure shape, size and surface chemistry, luminescence (emission spectrum, lifetime, efficiency and stability) and electrical conductivity. These materials will be applied to multi-color lighting, sensing, and photovoltaics.
The first step is the control of silicon nano-structures in order to get appropriate luminescence properties. We have studied porous nano-silicon (PSi), in a view to understanding the relationship between the PSi porosity and the optical absorption energy.
A new method of determination of optical constants of electrolyte-impregnated PSi using photocurrent analysis was shown. It has several advantages over other methods: easy implementation and ultimate preservation of nano-structure mechanical integrity and surface chemistry, for any porosity and layer thickness.
The porosity and spectral dependence of the quantum confinement in the absorption spectra were clearly observed from chemical dissolution of PSi. The study also revealed differences between red and blue emissions. For red emission, quantum confinement was easily observed whereas for blue emission, porosities in excess of about 0.8 was required. These results will be useful for the search of methods to get red to blue emission from PSi.
The method used also allowed the determination of the dissolution rate of silicon in various HF-based solutions, which is an interesting by-product of this research.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
3: やや遅れている
理由
The careful implementation of the studies described in the summary required more time than initially estimated, in part because it appeared even more interesting than originally thought. As a result, more fundamental results could be extracted from them, which required additional experiments and simulations.
The use of anodic oxydation to tailor the sizes ofthe nanostructures in porous silicon was delayed because the first technique (chemical dissolution in HF) was very interesting from the fundamental point of view and we wanted to get all the benefits from it before moving to this second technique.
From the knowledge acquired so far, we can now progress confidently towards the achievement of multicolor light emission from porous silicon and also from powders of single nanocrystals.
We have already started a study of the control of sizes of silicon nanocrystals in powder form using a technique similar to that shown in the past year. Also, we have started a study of photo-dissolution of porous silicon in order to control the structure sizes.
These two studies have progressed significantly, but more detailed studies are needed and are being carried out. In particular, simulations are now being carried out.
In parallel, the study of electroluminescence, which was planned on the second year, was initiated. Experimental setups have been installed and are now ready.
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| 今後の研究の推進方策 |
The research will continue as planned.
The control of the nano-silicon size will be carried out using photo-dissolution and selective oxidation of nano-silicon.
Electroluminescence (EL) devices based on bipolar carrier injection will be pursued. Ways to increase the porous silicon conductivity will be studied. The balance of electrons and holes injection and flow will be optimized.
Stabilization of nano-silicon and enhancement of nano-silicon conductivity will be studied, using (i) high-pressure water vapor annealing, which is the best stabilizing method to date for porous silicon and (ii) chemical modification of nano-silicon surface to replace Si-H bonds by more stable Si-C bonds.
Plasmonic structures for improving the luminescence characteristics of nano-silicon will be studied.
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