Femtosecond dephasing in porous silicon

Abstract We have performed non-degenerate four-wave mixing on free-standing porous Si samples. Within the framework of an idealized inhomogeneously broadened two-level system, values of 20 fs for the dephasing time are obtained for different porosities. Fast energy relaxation times are found in the range 1.5–3.5 ps for 64–73% porosities, respectively. They are attributed to carrier thermalization within the band tails, originating from porous silicon nanocrystallites and their surface states. © 1997 Elsevier Science S.A.