Photoemission study of porous silicon

We report x-ray photoelectron spectra from a porous silicon film (PSF) with a photoluminescence peak at 1.8 eV, as a function of argon ion etching time to probe the composition in the surface and the subsurface regions. The results clearly indicate that the surface layer is essentially a fluorine admixed SiO₂ phase, while the Si:O:F composition of the subsurface region 2:1:0.2. With the possibility of the existence of hydrogen in this composition it appears that beyond the highly oxidized surface, PSF is a fluorine substituted siloxene derivative, which can be responsible for the visible photoluminescence.