Picosecond dynamics of photoexcited carriers in free-standing porous silicon

Abstract

We study the ultrafast dynamics of photoexcited carriers in luminescent free-standing porous silicon at room temperature using the experimental 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 slower 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 (bimolecular recombination coefficient of 10 −10 cm 3 s −1), while the slower component is likely to be due to recombination via surface states.