A NONDESTRUCTIVE STUDY OF THE MICROSCOPIC STRUCTURE OF POROUS SI

The microscopic structure of porous Si films formed on different p-type doped substrates has been investigated by Raman spectroscopy. From a detailed line shape analysis of the Raman phonon peak, nanocrystal size distributions are obtained. These distribution functions depend on different sample parameters like the porosity and the doping level of the substrate, but are also influenced by the current density during the formation process. On thick samples, a change in the microscopic structure with depth is observed. This is due to a further chemical thinning close to the surface and to the limitation of the diffusion of reactive species from the deeper lying regions through the pores.