LOCAL-STRUCTURE OF POROUS SILICON STUDIED BY MEANS OF X-RAY-EMISSION SPECTROSCOPY

The paper presents a comparison between Si L-2,L-3 X-ray emission spec tra of porous silicon (P-Si) and of spark-processed silicon (sp-Si). B oth types of Si-structure display strong photoluminescence in the visi ble range 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 emis sion spectra of porous Si prepared from n(-)-Si display a higher conte nt of SiO2. For spark-processed Si the Si L-2,L-3 X-ray emission spect ra reveal a much stronger degree of oxidation which extends to depths larger than 10000 Angstrom. Furthermore, the chemical state of silicon atoms of sp-Si measured at the center of the processed area is close to that of silicon dioxide, and it has an influence on the photolumine scence energy. Specifically, green photoluminescent sp-Si shows a high er degree of oxidation than the blue luminescent specimen. However, th e depth of oxidation consistently decreases in areas with weak or no F L. Possible origins of the observed photoluminescence are discussed.