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 measuremen ts 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 structur al information on all luminescent and nonluminescent Si sites. On the contr ary, PLY is able to probe the local structure near the light emitting sites , and to monitor the modifications induced by current density changes durin g the sample preparation. PLY-EXAFS shows that the luminescent Si nanostruc tures are smaller and more disordered than the average structures of the po rous layer probed by TEY, suggesting that the luminescent sites are located at the surface of the nanostructures. (C) 1999 American Institute of Physi cs. [S0003-6951(99)03010-7].