Microstructural characterization of porous silicon for use in optoelectronic devices

Spectroscopic ellipsometry in the mid infrared spectral range, Raman scattering and TEM measurements on (100) oriented p+ and n+-type porous silicon (PS) samples were carried out. Porosities of 68% and 48% for p+ and n+ wafers, respectively, and thicknesses of 27.6 $\mu $m and 14 $\mu $m with the same extinction coefficient k = 0.1 were determined from spectroscopic ellipsometry. Raman scattering measurements show that the resultant surface morphology of the PS layers consists of irregular and randomly distributed nanocrystalline Si structures. Using the phonon confinement model, the diameters of Si nanocrystallites have been estimated as 8 and 3 nm for p+ PS type and 12 and 5 nm for n+ PS type. Transmission electron microscopy shows clearly defined pores with sizes ranging from 15 to 35 nm, inhomogeneously distributed along the PS surface. We demonstrate that the filling of the PS pores by organic material (Rhodamine 6G) brings about important enhancement on photoluminescence intensity