Micro-Raman study of free-standing porous silicon samples

Micro-Raman spectroscopy has been employed for the characterization of a se t of free-standing porous silicon samples with different degrees of porosit y, fabricated by electrical anodization of n(+) Si wafers. A broadening and a shift toward lower energy of the transverse optical silicon phonon mode have been clearly observed, indicating the presence of nanometer-sized crys talline structures. In particular, higher porosity samples reveal an inhomo geneous structure characterized by a spread of the nanocrystal size as a fu nction of the region under investigation. The photoluminescence properties of samples produced with similar fabrication parameters, displaying both a blue and a red band, seem to be in agreement with the nanocrystal dimension s derived through micro-Raman spectroscopy. (C) 1999 American Vacuum Societ y. [S0734-211X(99)07102-4].