Porous silicon prepared from p− and p++ bulk silicon

Macro and meso-porous silicon (PSi) samples were prepared by electrochemical anodisation of p^- and p⁺⁺ doped silicon wafers in hydrofluoric acid (HF) based electrolyte under galvanostatic conditions. Anodisation time and current were varied in order to obtain different PSi morphologies. Samples were characterized by scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and Raman spectroscopy. Samples prepared on p^- type substrates were macro-porous, showed visible photoluminescence and no observable phonon confinement in Raman spectrum. Porous silicon prepared on p⁺⁺ type substrates was mesoporous, showed no observable photoluminescence and intense phonon confinement was observed in their Raman spectra. Silicon nanocrystal dimensions in PSi samples obtained from photoluminescence and phonon confinement models were correlated with silicon electrochemical dissolution valence n_d. A surface morphology instability is identified in case where electrolyte is more conductive than the silicon substrate.