RTA effects on the formation process of embedded luminescent Si nanocrystals in SiO2

It is well known that Si ion implantation into SiO₂ and subsequent high temperature anneals induce the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of rapid thermal annealing to enhance the photoluminescence as well as those to induce low temperature formation of luminescent Si nanocrystals have been investigated. Ion implantation was used to synthesize specimens of SiO₂ containing supersaturated Si with different concentrations. 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 tube furnace to induce Si precipitation. Photoluminescence spectra were measured at various stages of anneal processes. The luminescence intensity is strongly enhanced with a rapid thermal annealing prior to a conventional furnace anneal. The luminescence intensity, however, decreases when rapid thermal annealing follows conventional furnace annealing. It is found that the order of heat treatment is an important factor in intensities of the luminescence. Enhancement is found to be typical for low dose samples. Moreover, the visible photoluminescence is found to be observed even after conventional furnace anneal below 1000 °C, only for rapidly thermal annealed samples. Based on our experimental results, we discuss the mechanism for the enhancement of the photoluminescence, together with the mechanism for the initial formation process of Si nanocrystals.