Soft-X-ray fluorescence of porous silicon: Electronic structure of Si nanostructures

The electronic structure of porous Si is investigated using soft-X-ray fluorescence spectroscopy. Significant changes are observed as compared to bulk Si, which we interpret as due to altered electronic structure in the Si nanostructures. By imposing standing wave boundary conditions on the valence band wave functions, we calculate the fluorescence spectrum for thin Si sheets of different orientations. For a (100)-oriented sheet, the calculation is in good agreement with the experimental spectra, suggesting that the nanostructure in porous Si is predominantly in the form of thin Si (100)-type sheets.