Picosecond and millisecond dynamics of photoexcited carriers in porous silicon

Abstract

We report on a detailed study of the dynamics of photoexcited carriers in red-emitting porous silicon at room temperature after excitation by 532-nm picosecond laser pulses. Experimental techniques of time-resolved absorption (pump and probe) and photoluminescence are used to cover a very large time interval ${10}^{\mathrm{\ensuremath{-}}11}$--${10}^{\mathrm{\ensuremath{-}}4}$ s. The dynamics exhibits fast and slow components. The fast component (\ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}10}$ s) is interpreted as a bimolecular recombination of free carriers in the core of nanometer-sized silicon nanocrystallites, and the slow component (\ensuremath{\sim}${10}^{\mathrm{\ensuremath{-}}4}$ s) originates in the recombination of carriers rapidly trapped in the surface localized states. We propose a rate-equation model which enables us to describe well the complete photoexcited-carrier dynamics from picoseconds to hundreds of microseconds. Our results strongly support the key role of localized states on the surface of a Si network in the steady-state red photoluminescence of porous silicon. \textcopyright{} 1996 The American Physical Society.