Investigations of the electron energy structure and phase composition of porous silicon with different porosity

Energy structure of the valence and conduction bands together with phase composition of porous silicon (por-Si) obtained at different etching times were investigated using ultrasoft X-ray emission spectroscopy (USXES) and X-ray absorption near-edge structure (XANES) techniques. USXES and XANES spectra represent local partial density of states in valence and conduction band, correspondingly. XANES data were obtained with the use of synchrotron radiation at synchrotron BESSY II. Porous silicon layers were obtained on different types of single-crystalline silicon (100) and (111) substrates by standard electrochemical etching in HF solution with etching times from 1 to 10 min. USXES and XANES investigations show formation of Si nanocrystals covered by amorphous phase together with nonstoichiometric silicon sub-oxide SiOx, (x similar to 1.3) in the surface layers. XANES investigations show that the increase of sample porosity leads to the shift of conduction band edge to the higher energy range that corresponds to increase of the band gap width in porous silicon up to similar to 1.4 eV. (c) 2006 Elsevier B.V. All rights reserved.