PICOSECOND AND MILLISECOND DYNAMICS OF PHOTOEXCITED CARRIERS IN POROUS SILICON

We report on a detailed study of the dynamics of photoexcited carriers in red-emitting porous silicon at room temperature after excitation b y 532-nm picosecond laser pulses. Experimental techniques of time-reso lved absorption (pump and probe) and photoluminescence are used to cov er a very large time interval 10(-11)-10(-4) a. The dynamics exhibits fast and slow components. The fast component (similar to 10(-10) s) is interpreted as a bimolecular recombination of free carriers in the co re of nanometer-sized silicon nanocrystallites, and the slow component (similar to 10(-4) s) originates in the recombination of carriers rap idly trapped in the surface localized states. We propose a rate-equati on model which enables us to describe well the complete photoexcited-c arrier dynamics from picoseconds to hundreds of microseconds. Our resu lts strongly support the key role of localized states on the surface o f a Si network in the steady-state red photoluminescence of porous sil icon.