FEMTOSECOND DEPHASING IN POROUS SILICON

We determine dephasing times T-2 in free standing porous silicon sampl es using nondegenerate four-wave mixing. Within the framework of an id ealized inhomogeneously broadened two-level system, values of 20 fs fo r different porosities are obtained. Fast energy relaxation times are found in the range of 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 sta irs. (C) 1996 American Institute of Physics.