RELEVANCE OF THE CARRIER TRANSPORT CHANGE IN POROUS SILICON AT THE ONSET OF ONE EXCITED PAIR PER CRYSTALLITE

We report on the first experimental observation of transient free-carr ier absorption-detected gratings in highly-luminescent porous silicon membranes. The sloping changes on 400 mu s long decay scale are observ ed below the injection onset for one excited electron-hole pair per na nocrystallite which are related to a notable shortening in the microse cond recombination form. A preliminary microscopic model for the dispe rsive recombination is suggested including the photoinduced fraction o f uncorrelated carriers, which recombine according to a power decay, i n contrast to the excitons which recombine according to a stretched ex ponential. At low excitation, we extract the upper limit of exciton di ffusion coefficient and diffusion length as D = 3.4 X 10(-5) cm(2) s(- 1) and L = 315 nm. (C) 1997 Elsevier Science S.A.