Structural study of porous silicon and its oxidized states by solid-state high-resolution 29Si NMR spectroscopy

Si-29 nuclear magnetic resonance spectra were measured to characterize porous silicon structures. Si-29 nuclei close to surface were selectively detected both in cross-polarization and non-cross-polarization spectra. The spectra were different from those for amorphous silicon and amorphous hydrogenated silicon. Therefore porous silicon is different from amorphous materials in the structural character. The resonant peaks were, however, much broader than the peaks observed for crystalline silicon. There exists distribution of bonding conformation in the porous silicon layer. The origin of the linewidth in the NMR spectra has been discussed. The contribution of each broadening mechanism to the width has been estimated theoretically and experimentally. The Si-29 NMR spectra for oxidized porous silicon species have been assigned as follows: - 50 ppm due to O2SiH2, - 85 ppm due to O3SiH, - 111 ppm due to SiO2, and - 101 ppm due to Si(OH)(x) or Si-29 located between OySiHx and SiO2. The signals of SiHx species have been assignable to -85 and - 94 ppm; however, further study should be done for the detailed assignment. [S0163-1829(98)03426-2].