X-RAY-EMISSION SPECTRA AND THE EFFECT OF OXIDATION ON THE LOCAL-STRUCTURE OF POROUS AND SPARK-PROCESSED SILICON

The paper presents a comparison of Si L(2,3) x-ray emission spectra of porous silicon (P-Si) and of spark-processed silicon (sp-Si). Both ty pes of Si structure display strong photoluminescence in the visible ra nge of the spectrum. Porous samples were prepared by anodization of n( -) and p(+) Si wafers. Whereas for the P-Si processed from p(+) Si the presence of some amorphous silicon is detected, the x-ray emission sp ectra of porous Si prepared from n(-) Si display a higher content of S iO2. For spark-processed Si the Si L(2,3) x-ray emission spectra revea l a much stronger degree of oxidation which extends to depths larger t han 10 000 Angstrom. Furthermore, the chemical state of silicon atoms of sp-Si measured at the centre of the processed area is close to that of silicon dioxide, and depends slightly on the emission maximum. Spe cifically, green-photoluminescing sp-Si shows a higher degree of oxida tion than the blue-luminescing specimen. However, the depth of oxidati on consistently decreases for areas with weak photoluminescence and wi thout photoluminescence. Possible origins for the photoluminescence ar e discussed.