RAMAN-SCATTERING AND NUCLEAR-SURFACE CHARACTERIZATION OF AGED POROUS SILICON

Aged porous silicon layers (similar to 1 mu m thick) have been characterized both by optical spectroscopy (Raman scattering and photoluminescence) and by nuclear surface techniques (Rutherford backscattering, elastic recoil detection, and nuclear reaction analysis). Samples with 85% and 70% porosity were analyzed after exposure to air for 1 month. Both these aged porous silicon layers emit visible light, but their luminescence shows dissimilar spectral features while their Raman scattering suggests a dissimilar microstructure. Chemical analyses indicate the presence of carbon and hydrogen at the porous surface, besides a surprisingly different oxygen concentration. A correlation between the structural and compositional results is attempted to account for the observed light emission spectra. In particular, the relative blue shift of the luminescence peak of sample with lower porosity is attributed to the stronger consumption of silicon nanocrystals operated by the silicon oxide formation during the aging process. (C) 1995 American Institute of Physics.