Ultrafast decay dynamics of luminescence in porous silicon

Ultrafast decay dynamics of luminescent porous silicon has been studied with a picosecond-spectroscopic technique. We have observed that the surface structure of the Si microcrystals changes the picosecond carrier dynamics: picosecond luminescence decay becomes faster with increasing hydrogen termination on the surface of a Si microcrystal. We have also observed the redshift of the luminescence peak in the initial decay stage. This shift disappears with increasing hydrogen termination. These results suggest that there are two luminescent states in Si microcrystals: a weak luminescent quantum-confinement state (Si microcrystal core) and a strong luminescent surface state. Surface treatment by hydrogen termination on Si microcrystals influences the transfer rate between the two states and changes the origin of luminescence from the surface state to the quantum-confinement state.