Control of microstructures of silicon nanocrystals by ion implantation and their application for optical devices.

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Si ion implantation into Si0_2 and subsequent high temperature anneals induce the formation of embedded luminescent Si nanocrystals. The potentialities of rapid thermal annealing (RTA) to enhance the photoluminescence (PL) as well as those to induce low temperature formation of luminescent Si nanocrystals have been investigated. Si ion implantation was used to synthesize specimens of Si0_2 containing supersaturated Si. The implanted samples were rapidly annealed only for a few minutes. After that, in some cases before that, the samples were annealed for a few hours using a conventional furnace to induce Si precipitation. PL spectra were measured at various steps of anneal processes. The luminescence intensity is strongly enhanced with RTA prior to a conventional furnace anneal. The luminescence intensity, however, decreases when RTA follows conventional furnace annealing. It is found that the order of heat treatment is an important factor in intensities of the luminescence. Enhancement is also found to be typical for low dose samples. Moreover, the visible photoluminescence is found to be observed even after furnace anneal below 1000 ℃, only for RTA treated samples. In forming the luminescent Si nanocrystals in a Si0_2 matrix from supersaturation, decomposition, segregation, diffusion, nucleation, aggregation, growth and crystallization processes are clearly important. As a result of diffusion limited segregation, a number of small aggregates will be formed and they act as a nucleation point.In the present research project, we have found that the luminescence intensity is strongly enhanced with a rapid thermal anneal prior to a conventional furnace anneal and the luminescence intensity decreases with a rapid thermal annealing after a conventional furnace anneal. Moreover, a post implantation rapid thermal anneal prior to a furnace anneal is effective to achieve low temperature formation of luminescent Si nanocrystals.