On the sensitivity of the x-ray excited optical luminescence to the local structure of the luminescent Si sites of porous silicon

X-ray excited optical luminescence (XEOL) has been recorded in a wide x-ray energy range to obtain the extended x-ray absorption fine structure (EXAFS) at the Si K edge of porous silicon. A comparison between EXAFS measurements carried out simultaneously in photoluminescence yield (PLY) mode and in total electron yield (TEY) mode on red and orange porous silicon samples is presented. Experimental results suggest that TEY provides average structural information on all luminescent and nonluminescent Si sites. On the contrary, PLY is able to probe the local structure near the light emitting sites, and to monitor the modifications induced by current density changes during the sample preparation. PLY-EXAFS shows that the luminescent Si nanostructures are smaller and more disordered than the average structures of the porous layer probed by TEY, suggesting that the luminescent sites are located at the surface of the nanostructures. (C) 1999 American Institute of Physics. [S0003-6951(99)03010-7].