PICOSECOND DYNAMICS OF PHOTOEXCITED CARRIERS IN FREESTANDING POROUS SILICON

We study the ultrafast dynamics of photoexcited carriers in luminescen t free-standing porous silicon at room temperature using the experimen tal techniques of picosecond absorption and luminescence spectroscopy. Both the luminescence intensity and transient absorption signals show a fast decay on the scale of hundreds of picoseconds, followed by a s lower nanosecond decay. We identify the faster component of the decay as being due to a bimolecular recombination process in the core of Si nanocrystallites with a quasi-direct gap energy structure (biomolecula r recombination coefficient of 10(-10) cm(3) s(-1)), while the slower component is likely to be due to recombination via surface states.