Relevance of the carrier transport change in porous silicon at the onset of one excited pair per crystallite

Abstract We report on the first experimental observation of transient free-carrier absorption-detected gratings in highly-luminescent porous silicon membranes. The sloping changes on 400 μs long decay scale are observed below the injection onset for one excited electron–hole pair per nanocrystallite which are related to a notable shortening in the microsecond recombination form. A preliminary microscopic model for the dispersive recombination is suggested including the photoinduced fraction of uncorrelated carriers, which recombine according to a power decay, in contrast to the excitons which recombine according to a stretched exponential. At low excitation, we extract the upper limit of exciton diffusion coefficient and diffusion length as D =3.4×10 −5 cm 2 s −1 and L =315 nm. © 1997 Elsevier Science S.A.